OTOH, Colorado seems to be the epicenter of extreme driver/cyclist mutual hatred. (not saying this is true, just that plenty of incidents make the news).

Maybe that's because of too many conflicting rights and people who won't give to get.

Here in NY, riding 2 abreast is also legal, but cyclists doing so have to break down to single file to allow passing.

BTW- I don't see it as a question of legal tolerance, but of conduct. It seems that some people rarely, if ever, have negative encounters with motorists and for others it's an almost daily occurrence. I'm sure that some or even much of that can be chalked up to regional differences, but suspect that some can be chalked up to the individuals involved.