You have this backwards - cops that know the law and restrict their actions to remain within it at all times are the very, very limited exception. 95%+ of cops will just push the limit as far as they can go - they have nothing to lose except having charges dismissed on arraignment. They bet you won't push a false arrest suit against them and just keep a bucket of BS handy to justify their catch-all charges of 'disturbing', 'disobeying', etc.

Frankly, I'd like to see fully empowered citizen review boards being given the power of oversight and ability to suspend or terminate any member of their police force who is found to act in a manner which is not fully and completely inside the intent and letter of the law.