More general reasons: In an adversarial system, unless both sides get a vigorous attorney, the system doesn't work. In a non-adversarial (or inquisitorial (not

More general reasons: In an adversarial system, unless both sides get a vigorous attorney, the system doesn't work. In a non-adversarial (or inquisitorial (not that one!)) system, unless the courts give a lot of time to people who are probably guilty and generally scummy, the system doesn't work. Unwritten laws are inconsistently applied as a result of gross bias and favoritism. If you have an unwritten law which is consistently applied, you have a written law. See below. Written laws can be gamed. If you have a written law that can't be gamed, you actually have an unwritten law. See above. We want it to be fairly difficult for the state to punish people. The kinds of people who tend to be accused of serious crimes aren't the kinds of people most of us here would invite out for drinks. Therefore, we see a lot of people we wouldn't associate with getting the kind of benefit of the doubt we don't give to waitstaff at a restaurant. The system working as intended makes for lousy fiction, unless it somehow involves someone getting off on a technicality. The fact the technicality was written into the Constitution or is otherwise fundamental to a good, orderly, and just society gets... elided a bit. And, of course, there are a lot of assholes in the world, there are a lot of JDs in the world, there are no real anti-asshole filters on the "earn a JD" process, so there are a lot of assholes with JDs in the world.