You really need to watch the first movie, Dirty Harry (1971), to understand where Callahan is coming from. He's a Cowboy Cop who tries to work within the system, but when the system fails to punish the guilty, he becomes a loose cannon. He believes that it's a perversion of justice to focus on upholding the civil rights of criminals, while ignoring the civil rights of their victims.
Harry seems to treat his various adversaries as "outlaws" in the original sense of the word: In the Middle Ages, someone who was officially declared an outlaw was literally "outside the law" — meaning he could no longer claim any rights or protection under the law, and was thus fair game for anyone who might kill or capture him.
edited 30th Sep '17 10:32:42 AM by pwiegle
This Space Intentionally Left Blank.It should be noted that when Harry was given the chance to join the paramilitary death squad of ex-Special Forces soldiers turned motorcycle cops, the titular "Magnum Force" in that film, Harry not only said no, he killed every one of them, and their boss. Harry believes in the law, and administers it without fear or favour, to the detriment of his career.
Harry once said: "There's nothing wrong with shooting, as long as the right people get shot." The Magnum Force was shooting indiscriminately, mowing down innocent bystanders along with their intended targets. This was one reason why Harry despised them, along with their heavy-handedness. ("What's next? Soon you'll be executing people for letting their dog piss on the neighbor's lawn!")
Remember that these films were made in the 1970s, when urban decay, civil unrest, and skyrocketing crime rates were typical. Police were overworked and understaffed, and the courts were clogged up with cases. While liberals were adamant about protecting the rights of the accused, conservatives wanted to declare martial law and use the military to clean up the cities.
edited 1st Oct '17 4:50:57 AM by pwiegle
This Space Intentionally Left Blank.Oh, if you wanted to get technical, you could talk about conservative Nixon voters yearning for "law and order", especially if law and order consists of bad guys getting shot up. See also Joe, which got a lot of Misaimed Fandom.

Can anyone explain the finer points and ideas that the films express thorughout the series? I watched Magnum Force, Sudden Death, The Enforcer and Dead Pool myself but I may need to rewatch them as well as the first film to understand the themes. Can anyone explain the conflict in the films? And what makes Callahan different from the people he fights against?
"Fan, a Mega Man character."