This is it. Law enforcement often doesn't bother with cyclists. If you don't endanger anyone or make anyone nervous with your speed or proximity and you aren't likely to get caught or make a bad example, then you're not doing any harm. A lot of this is related to the culture of your locality. In the midwest and west of the US, people generally follow the law. NYC is the wild west, where traffic flow of cyclists and pedestrians resembles water running down a hill. It finds all possible directions and spaces and never stops flowing. If a westerner tells me I'm doing something terribly wrong, it's as stupid as me telling them that they should run red lights.

I am one of the most cautious riders I see in Manhattan. When I come to a red light, I stop. Then after the cross traffic is exhausted and there are no pedestrians near me, I cross very slowly. I turn my head left and right repeatedly without stopping to make sure I'm not endangering anyone or even making anyone nervous. I make it obvious, with my constant head turning and my slow pace, that I will not make anyone change course or direction as a result of the path I'm taking.