This may likely have contributed To DJ AM's death. After surveying a horrific fatal plane crash that killed everybody on board, but him and rocker Travis Barker. AM ( Born Adam Goldstein), a former addict decided to help other addicts via a reality show. During filming he began to be uneasy in the situation as just holding the drugs felt tempting, Goldstein later died from a drug overdose.
Raoul Wallenberg. A Swedish diplomat, who saved countless of Jews and other persecuted minority members from extermination camps, was widely known as a philantrope - and was hijacked just before the end of WWII by the Soviets. The Soviet intention was to extort the Swedish government by keeping him as a hostage and exchange him for Soviet spys caught in Sweden. When Sweden refused to comply, he disappeared.
One example is that of Hugo Alfredo Tale-Yax, a homeless man in NYC who attacked a mugger that was robbing a woman and succeeded in driving him off and allowing her to flee. He was stabbed for his troubles and bled to death on the sidewalk while about two dozen people walked by.
Additionally, crooked, lazy cops have been known to pin crimes on the people who called them just because they are having a difficult time finding the real criminal. Calling the cops and, as a consequence, being asked to testify in court as a witness can make them a target.
And when it comes to gang violence, many potential witnesses will either not call the cops or refuse to testify in court, fearing that the gang member's allies will hunt them and/or their family/friends down for revenge. Street gangs knew about this and some have started to wear shirts with the phrase "Don't Snitch" (or a variation of it) on them to intimidate people into keeping quiet.
Whistleblowers. You typically lose your job, can't easily find another with your status, and this is the best case scenario without legal repercussions or death threats.
Supposedly there are laws against retaliation, but given how most companies hire you on an at-will basis, they'll just fire you anyway for another reason.
Oliver Sipple saved President Gerald Ford. The resulting media frenzy over his heroic act outed him as a gay veteran, leading to estrangement from his conservative family and numerous unsuccessful lawsuits to the media which later led him to kill himself.
A Mexican illegal alien while crossing the border stops to help a boy and his mother victims of a car crash, he gets detained and deported.
It is illegal in some states to top off parking meters in front of cars that don't belong to you, since it deprives the city of the money from a parking ticket.
In some jurisdictions, e.g. San Francisco, it's illegal to top off parking meters in front of cars that do belong to you. note This only applies to parking meters in zones with a time limit. i.e., If you've parked there for 30 minutes in a two hour zone, you can't top off a meter for the full two hours because you can be there for 2.5 hours
It is illegal (operating a taxi without a license) in some cities to advertise a free service giving people a free ride home if they had too much to drink. This is because being able to get a drunk person into your car to take where you want is a wonderful opportunity for the less-than-generous, but it also causes people to drive when they really shouldn't.
The fact that Good Samaritan Laws exist in the US is a result of this. There are cases where a person tried to sue the person who performed CPR or the Heimlich Maneuver on them. In some cases this is because the good samaritan may performed life-saving technique wrong, injuring the victim even more than they already are, while certain other life-saving procedures result in injuries even when done correctly note one example being CPR, which tends to result in broken ribs. Because of events like this, people hesitate to help someone that is in trouble, fearing they will be punished for just trying to help out or hurt the victim even more.
To this effect, there has never been a successful court case in the US against someone who was providing emergency aid in good faith.
In some emergencies, it really is preferable that non-experts not get involved, because they will either doom the victim or become new victims themselves. Drowning is a classic example. Don't jump into the water to rescue a swimmer in distress if you don't know what you're doing.
This notion is part of why enrollment of volunteers in Big Brother programs have fallen off in recent years.
The trope name is frequently quoted by Judge Judy, in cases where the plaintiff got screwed over by trying to help someone (usually by lending money to a deadbeat).
Read headlines at Fark.com and you'll eventually come across many of these.
Standing up to bullies that are picking on someone at school will likely get the bullies and their friends to come after you for your troubles. Similar to the robbery turn murder example above, this can result in other kids keeping quiet about the bullying incident or refusing to help out in fear that they will become a victim themselves. It gets worse when physical violence is involved.
During the 1996 Olympics in Atlanta, Richard Jewell noticed a bomb and reported it to the police. He was hailed as a hero at first, but because the police had no leads on the bombing suspect, they began to suspect and eventually charge Richard Jewell as the bombing suspect. He would be vindicated later when the real bomber - a serial bomber named Eric Rodolph - was linked to the bombing but wouldn't be captured until 2003. Richard Jewell ended up suing the media for slandering his name.
How about the poor girl who got expelled from her school, thanks to the school's No Tolerance Policy, because she was attending a party with alcohol...so she could pick up her drunk friends and drive them home safely.
One of Ted Bundy's favorite methods of luring his victims was his Wounded Gazelle Gambit—he'd put his arm in a sling or walk around with crutches and approach lovely young women, asking for help in carrying books or parcels to his car. As one crime writer so sadly put it, "The cost of their altruism was their lives".
This trope is one of the many reason why churches (and people attending church) are actually extremely common theft targets.