The First Amendment of the United States Constitution provides Americans with the right of Freedom of Speech as well as some other core ideals (among other things, including Freedom of Religion and Freedom of Establishing of Religion, as well as the Freedom to Peacefully Assemble and Freedom of the Press). Since the primary scope of this article is about Freedom of Speech, we will focus on that aspect, but given the broadness of that topic, it's easy to file those ideas under Freedom of Speech. And if there is one word to describe the United States' version of Freedom of Speech, it is Broad. Wikipedia notes that the United States has some of the most liberal Freedom of Speech laws in the entire world, with only a few ways to actually be punished for offensive speech. It may come as a shock to many other people from Western Societies that have Free Speech, but not to the extent of the United States. The United States' First Amendment is the most likely culprit in divergences in The Common Law from the rest of Common Law states and is also the reason most countries around the world find Americans to be loud and opinionated. It's also one of the reason why Americans have a large range of hot button issues. Americans are proud of their Freedom of Speech and exercise it every opportunity they can, as much as they can.
The Market Place of Free Ideas: History of American Freedom of Speech
England and her Colonies
During the initial colonization of the original 13 states, England operated under Seditious Libel, preventing the common man from criticizing the government, arguing that it was necessary for functional government that the people have a good opinion of it. While these laws were in force in the American colonies, they were never used at the same rate as their English counterparts and only really used for blaspheme laws stateside (though the odd case turns up from time to time that was actually directed at the Government). Because of this, for nearly 100 years between 1607 and 1700, free speech had been allowed to gain traction among the colonials.
Then, in 1733, a newspaper publisher named John Peter Zenger wrote several articles about the newly appointed Governor of New York, who had thrown a popular Justice off the Supreme Court and installed judges and court officials who would toe the line for him. The Governor had charges of Seditious Libel brought up against Zenger. Zenger's second lawyer, Andrew Hamilton (his first was thrown off the case after being held in contempt of court for defending a man who was known to disagree with the court!), did argue that libel must be false (in this particular case, it was not... the jury practically saw it happen before their eyes) and did get a Jury-Nullification (Basically, not guilty because the law he was accused of breaking was wrong to exist) though its more commonly thought that the jury granted the verdict because they just didn't like the Governor.
The result was well celebrated and Hamilton was praised by many Revolutionaries as the "Dawn Star of the Revolution". The news of the case traveled quickly, and while praised by the colonists, the British governors of the colonies began to crack down harder on Seditious Libel up until the Americans got got some revolutionary ideas about that.
The Early United States
It is important to note that the United States has not always been the bastion of free speech. Under John Adams, America adopted four laws collectively known as the Aliens and Sedition Acts of 1798. The "Aliens" part derived from three laws that gave the president greater powers to control immigration into the United States (namely, it raised the length of residency before one could be a citizen from five years to fourteen years, allowed the President to deport non-citizens who threatened the peace of the United States at any time, and deport those from hostile nations during times of war.). The Seditions Act when viewed through through historical lens as legalizing Seditious Libel in all but name. In contemporary times, it was a seen by the Democratic-Republican party as law used by the Federalist Party to silence opposition politics and immigrants (it wasn't helped that most immigrants at the time politically aligned with the Democratic-Republican party). It ultimately lead to John Adam's defeat by Thomas Jefferson who then pardoned everyone prosecuted under the Seditions Act, paid back compensations for jail time and fines, and ultimately let it and all but one of the other three acts die with out renewing the legislation. This would be the only time that Free Speech was questioned until the 20th century.
The First World War: A Clear and Present Danger
For the next 120 years or so, the Supreme Court refused to hear cases on the merits of free speech claims. This changed in 1918 when congress passed a series of amendments to the 1917 Espionage act that are typically refered to as the Sedition Act of 1918 note . These amendments basically criminalized saying things that were disloyal to the United States government but only "in times of war". Several challenges did make their way to the Supreme Court, which would set the movement of American Jurisprudence for the next century. Justice Oliver Wendel Holmes wrote two opinions in 1919 that became part of America's Free Speech lexicon: The first was "Clear and Present Danger" which the courts later dropped in favor of "Imminent Lawless Action" as well as "The Market Place of Ideas", which most critics found to be the best argument made in the case, despite it being the dissent note . While the former was cleaned up, because the latter is decent opinion, it is not a legal force. That said, it has widely entered the American lexicon and is generally the idea behind most legal opinions on Free Speech in the 20th century.
The whole history serves to make American Free Speech laws both Older Than They Think and Newer Than They Think. The concept of criticizing the government predates the founding fathers by centuries, but the degree to which it has been implemented is almost a century old in and of itself and still very much untested waters with the more liberal ideas are much younger than that.
What Qualifies as Free Speech
As a rule, when determining if something qualifies as Protected Free Speech, the courts err on the side that such Speech and the burden of proof is on the argument that such speech is unprotected. With that being said, The United States breaks all speech into three categories:
Core Political Speech
While the ability to speak ones mind freely about politics and the opinions of the day is generally the primary speech defined by this category, it does not necessarily have to do with politics. It just so happens speaking ones mind to politics is generally the most controversial form of free speech, hence the name. It could also protect your opinion on a brand or ability to discuss your opinions on various uses of narrative devices in media products and if such a use is proper. This is the most protected form of the speech and requires the strictest scrutiny when making laws that put restrictions on speech (more on this in a bit). This generally covers spoken and written words unless the speech falls into the next category.
Essentially, speech that is made in order to make a profit. It is largely protected like the above, but can be restricted by the government with less burden. Usually this is in the form of various Legal Disclaimers and Truth in Advertising (or anti-Fraud laws) laws that must be included in the advertisement. Beyond that, the company can advertise however they wish, be it serious or funny or logic defying.
When is Speech not Speech? Although the Constitution does not expressly say so, expressive speech, or speech that involves symbolic or non-verbal communications is also protected. This includes things like Burning the Flag note , performance art, traditional physical art, and even codes, computer codes, and math and formulas. This category is protected based on how it falls in the above two categories, but to the same degree. This is also the freedom of speech that giving money to political campaigns falls under. Even not partaking in speech at all is still a form of protected speech.
Restrictions on Speech
To start off, the rules of Freedom of Speech only affect government entities and as such, free speech may be restricted by a private person or organization on property they control (so no, if you get banned from a website for vandalism or abusive behavior, your First Amendment rights have not been violated). OR on employees who are acting as part of their job. The Government, as an employer, can make these restrictions on employees and some limited restrictions on government property, provided that they are acting as an investor entity in the property (such as post offices or airports).
In addition, the Government can restrict the exercise of Free Speech so long as such restrictions are content neutral, there is a compelling interest to enacting the restriction, and the restrictions are narrow and allow for alternative methods of free speech. A government is well within it's right to create ordinance banning protest in residential areas after a certain time, so people can sleep. They can also arrest protesters who are blocking traffic note . The above are content neutral, as they do not care about the message. It could be "God Bless America", the rule still applies. They have a compelling interest (citizens need to sleep, emergency vehicles need to get to emergencies in the quickest manner possible). They are narrowly tailored (Only in residential areas at designated hours/ only on public roads) and offer alternatives (you can protest during the day/with a permit).
Of course, the government has laid out some pretty specific forms of speeches which are not protected by Free Speech. It should be noted that while this list is longer than the types of Free Speech allowed by the United States, protected Free Speech is very very broad while the exceptions are all very narrow in their scope.
Fire in a Crowded Theater
Any speech that would incite "Imminent Lawless Action". The classic hypothetical is "Shouting Fire in a Crowded Theater", which would incite a panic and create a possible risk to those who are exiting the theater. If this is falsely done, it is not protected (goes without saying if there is a real fire... or very likely a real fire, please, let people know. But if you get your kicks out of watching people panic and do it without a fire, you're going to get yourself arrested). This also includes inciting riots or other criminal action, such as hiring a contract killer or asking someone to participate in a crime on your behalf.
Them's Fighting Words
Fighting Words are insults, slurs, or other forms of speech that are designed to make someone angry enough to breach the peace. It could be anything from a malicious Your Mom joke to a use of N-Word Privileges when you do not have them. This does not mean that offensive words in and of themselves are banned. In fact, no word, no matter how offensive, is banned by Fighting word Doctrine. Rather, it is the intent of the words in context of the situation AND that the attack is personal to some level. Westboro Baptist Church gets away with their actions because, while offensive, they are not attacking any one person by their speech. In fact, you can get into trouble if you punch them at a funeral. However, if you insult someone to their face to such a degree that they want to attack you, then you can be arrested for breach of peace from the ensuing Bar Brawl, even if you never threw a punch back.
Basically threats are taken real at all times. Threats of unlawful action are not considered protected speech (whether you were joking or not) and are taken very seriously, especially after certain events. The obvious interest is in the prevention of panic and disruption in addition to preventing first responders from responding to a real threat because they've had enough with your Hoaxes.
First responders will take any threats seriously and will respond as if the threat was real. Because until they confirm otherwise, it might as well be. Again, context is being everything, if it's clear you're joking, it's okay (not to mention local emergency services are routinely rolled out when a kid accidentally dials 9-1-1 as this serves the dual purpose of figuring out if the emergency is real or if the kid needs to be taught a valuable lesson so they know when to call and when not to call). This is for when it isn't clear. Most jurisdictions do have laws about calling 9-1-1 for non-Emergencies and will prosecute.
And even then, some things are just not funny, even if it was intent. Case in point, if you say anything that is interpreted as a threat to the President of the United States by the Secret Service, expect them to come a-knocking with some questions. Following Columbine, and 9/11 threats to shoot up a school or of more terrorist actions were met with very close scrutiny.
I'll know it when I see it.
AKA Depicting Sex
Even by Free Speech Laws, Obscenity laws are rather nuanced. Uniquely, the courts do not have a definition of what counts as obscene to meet any standard because, what's normal in Hollywood might not be kosher in Flyover Country. The quip of "I'll know it when I see it" was never about obscenity in general, but what would make a work softcore versus hardcore porn. It was just funny enough and summed up the general attitude of the supreme court on the larger matter. What is considered obscene is generally based on the average reasonable person would find obscene in that particular geographic/cultural region, which is can vary note . For example, most jurisdictions do have some law against public nudity and age at which pornography can be purchased, but few others can merit.
And while we're on porn, pornography is not allowed if it has no serious literary, artistic, political, or scientific value. And before you make Porn Without Plot cracks, the artistic merits of depicting people naked for no other reason than to depict them naked is good enough of a reason for the laws eyes. But most communities do not care for showing it in public places, which will get you into trouble. Also, while TV networks tend to be clean of this stuff because they do not want to fall into local laws about depictions of such material, whether or not The Internet Is for Porn has never been decided by the courts, and the accepted understanding is that the material is not obscene for the people who would frequent those sights.
There is one special case of obscenity law that is its own special limit...
The Supreme Court has ruled that the Government's interest in preventing the child abuse and trauma related to this particular obscenity far outweighs any of the possible artistic merits ascribed to it to protect it as free speech. Making, selling, buying, or owning anything pornographic with a minor involved in it are all illegal. 'Nuff said.
J. Jonah Jameson: I resent that! Slander is spoken! In print, it's libel.
One of the first major deviations of the United States Freedom of Speech from the rest of the world is that it's a lot harder to sue for defamation, be it libel or slander. Unlike other countries, in the U.S. a false statement is not defamation merely because of careless reporting and fact checking. It must be a falsehood, knowingly and maliciously presented as the truth. I.E. You don't have to know it's true at the time, but if you don't correct yourself once it becomes known to you, then your statement no longer enjoys Freedom of Speech.
And even if Spider-man wasn't so broke that he had to sell pictures to Jameson, if he were attempt to sue for libel, no doubt Jameson would point out that Spidey is a public figure. Under U.S. Laws, public figures have an even higher burden of proof for defamation cases, otherwise we wouldn't be able to have all the fun political satire that we enjoy. As Spider-man was quite the public figure, Jameson might have a strong defense (though saying he was terrorizing the crowd, as a headline, might be deliberate, Jameson was known for putting his opinions in the headlines, which isn't illegal, just very bad journalism).
Protected Speech does not allow for the communications of classified information with those who are not cleared to receive such information. In addition, it does not allow for the teaching of making explosives or other weapons if the teacher suspects the student will use them for criminal purposes. Speech made by employees of the government are not protected while they are on duty.
In addition, students in public schools are permitted full free speech rights, however, most school newspapers are not forums for free expression and are subject to censure by the government in the form of the teachers and faculty (if the paper is deemed a forum of free expression, however, it has no such power. This normally occurs at the University level though). Additionally, School Uniforms are not common in the United States as it is seen as obstructing freedom of speech in the form of clothing choices.
Finally, as noted above, the protection of free speech is not protected on private property, and you can be removed if you engage in some more disruptive speech that would be protected if it was in public.
A Special Note on Hate Speech
The United States is unique among the world as being the only developed liberal democracy without laws prohibiting hate speech or speech that is used to discriminate. The mere use of slurs or offensive words to a particular race, religion, nationality, sexuality, or sex are not on their own criminal acts in the United States, and which words are considered rude and which are not is not codified in any law. If you do not have N-Word Privileges, there is nothing stopping you from saying that word in public, from the stand point of the legal system. From a societal standpoint, you might face public outcry and scorn, but as many people have noted, the First Amendment gives you the Freedom of Speech, not the Freedom of Consequences of such Speech.
That said, as mentioned above, the common uses where this type of speech can fall under one of the above exceptions to free speech. If you say a slur while committing an unlawful act against a person can get you charged with a hate crime. This is not hate speech as the crime is prejudicial thoughts motivating criminal actions. In fact, a hate crime can be committed if you use nothing but politically correct or even are wholly inaccurate statements to describe your victim while you commit the primary offense against them. Again, it's the action and motivation, not the language, that are at odds with the law, since any speech related to committing or inciting others to commit criminal action is against the law. It's also is unrelated to minority status (in fact, one fifth of all hate crimes in the United States are committed against White people). It also can apply to political affiliation and in some jurisdictions, homelessness and even certain professions (Police Officers being a notable one.).
As to retaliation to hate speech, it depends on the context of the speech. If it was an insult meant to anger or offend a particular individual or individuals (as opposed to a broad community of people offended by the word) it is fighting words and you can be charged with crimes like disturbing the peace or inciting lawless action (i.e. the fight that breaks out because someone decided to punch you. This doesn't absolve them of their own crime of assault, but prosecutors may push for a lesser charge if they press at all). If you are not using them in this manner and are attacked for your trouble, legally, you are innocent.
I do not agree with what you said, but I will defend to the death your right to say it: Americans' Attitudes to Free Speech
They love it. Few issues are so apolitical in the United States as free speech (not that they're are not some charged opinions on the matter, this is America after all). And many Americans are loathed to side with the curtailing of Free Speech. Even organizations with detestable messages such as the KKK and Westboro Baptist Church are given the due note that while they might not like the message, they would prefer the organization keep on speaking their mind than the government shutting them down. The general reason is that, if the government can shut down a group they disagree with, then they can shut down speech that the opinions that they do agree with. As noted here and elsewhere, Americans can come off as loud and opinionated to the rest of the world, and that has certainly been fostered by the First Amendment freedom of speech.
Polling data is surprisingly revealing too. In a 2015 Pew Research Center poll of 38 countries, it found the United States was by far the most rabidly pro-Free Speech citizens in the country. 77% of Americans believe people should have the right to make offensive statements about their own religion publicly (compared to the global average of 35%) and 67% believe the same about offensive statements about minorities (Also 35% global average). 52% of Americans believe that people have the right to say sexually explicit statements which, may seem low, but is the second highest percentage in the world (70% of Spaniards believe) and only one of three to be 50% or higher (Poland being exactly 50%. The global average is 26%). And despite it being unprotected speech, the 44% of Americans believe in a right to call for global protest, as opposed to 25% global average. (This may have more to do with the United State's birth, which was pretty much the result of a giant violent protest.)
And despite how contentious American politics can appear, the right to criticize the government is so popular, it crosses party lines. Nearly 95% of all Americans believe in such a right, compared to a global average of 80%. In fact, it's so fundamental, it can make some strange bedfellows when this issue comes into play. It's not uncommon to see very left leaning organizations defending conservatives when they are being denied their free speech and vice versa. For example, when Bill Maher and Sean Hannity agree on very little politically, but when Maher was in trouble about his opinions about Islam, Hannity came to his defense, citing Maher's unwillingness to be silenced on the issue was "Good for America". And when conservative Ann Coulter was denied a venue for her speech, the famously liberal American Civil Liberties Union sided with her against UC Berkeley (see Strawman U for reasons why). In fact, the above cited statistics conclude only that Americans are more tolerant of people speaking offensive opinions, not that they agree it's okay to have such an opinion.
All that said, Americans are well aware that their tolerance of free speech has some darker shades to it. Neo-Nazism has found a safe haven in the United States (in fact, the American Nazi party is the strongest branch of said party. Lest it cause some concern, they still aren't in numbers great enough to do much of anything to American politics aside from existing), where such ideas are unappetizing to the country that likes to think they won that war. On the flip side of the coin, many Americans who hear of Germany's policy of No Swastikas find it in a somewhat moral grey area of approval (if they don't think it's white washing history, which it isn't). Again, it boils down to an uncomfortable feeling that a government that can ban something offensive can ban something I agree with. (Also, Nazis being the Acceptable Targets that they are, find themselves at the butt of many jokes in America and many Americans in Germany aren't sure just where the line between tasteless humor and illegal speech is in such cases. Modern Germans are make these jokes as well, but most Americans are first taken aback by the idea of Germans with a sense of humor at all.) The KKK and Westboro Baptist Church are also tolerated to exist, even though there are very choice words among the public about such actions. In fact, in a Supreme Court case (Snyder v. Phelps) that found in favor of Westboro Baptist Church, the Majority Opinion pretty much repeats that the court is only supporting the right of the church to say what it wants, not agreeing with what it says.
Of course, the obvious remedy to such hateful opinions is to counter with ones you do agree with. Through the discourse, it would be assumed that either the point of the unpopular opinion was rebuked in the minds of the public OR that the exchange of differing points of view allowed the two who were opposed to come to a positive version of Not So Different. The founding fathers believed, and the supreme court has affirmed, that there are no opinions so vile or hateful that they can broadly be banned from having a voice in a government by and for the people. For every "hateful" idea, take a look at things such as Fair for Its Day, which discuss some of the ideas that we see as beyond obvious to the point of stupid or racist with a modern perspective, yet were quite forward thinking for their time. For a less specific idea, it's the ability to say Seinfeld is actually funny when everyone else thinks "Seinfeld" Is Unfunny.
Notes: The OP is well aware that as an American, he is offering an internal perspective of the attitude of Free Speech. Even at that, it falls closer with the majority, as the whole point of the amendment is to protect the minority view, helpful, constructive, criticism and additions are greatly appreciated.