Atheism is sort of like animal rights. Many hunters belong to such groups as Ducks Unlimited, which are all for expanding wetland preservation to protect migrant birds.
PETA, on the other hand, is something far different. And far more radical by orders of magnitude.
And so you will find quiet, non-combative atheists in surprising numbers (even some who go to a church for social reasons). Many of these might more properly be called agnostics.
And so you will find the real toolcase full of wingnuts: Running into a catholic church dressed as nuns in drag, disrupting mass, and so on. I know a self-avowed atheist who actually joined in with Scientology for a long while - and saw no great conflict of interest, as his main agenda was a hatred of conventional christianity.