The level of ignorance here is very disappointing. It certainly shows a need to improve civics education in the United States.
The resources for the police, prosecutors and judges are simply not enough to enforce every crime committed. If there were no scarce resources, there would be police officers on every street making sure that nobody jaywalked.
So, the issue becomes one of who decides what to enforce, or one of prosecutorial discretion.
This is an excellent point and I'm happy to adjust my view of this kind of situation because of it, so thanks. I suppose the issue is more that American prosecutors behave like—and are—political figures in general than that they exercise this discretion for their own ideological or moral reasons in particular (which I'm sure police boards etc. do in Canada as well).
Frank is correct that it's absolutely necessary for prosecutors to exercise discretion, otherwise nothing would get done because the legal system just doesn't and can't have the capacity. The ideal would of course be for said discretion to be exercised in such a way as for it to always be clear to the hypothetical genuinely interested observer why the prosecutor took the course of action they did, and for this to both occur without undue pressure towards a particular outcome and reflect a reasonably consistent set of standards broadly shared by the community - and herein lies the problem. The logic of American politics at the moment is such that the legal system is in real danger of one day just not having a Hartian rule of recognition anymore, at least for a while.
