@FBM,
I agree that saying "I'm an atheist",
should not be confrontational.
Because atheist is a short hand description. The problem is that it can become perceived as a label.
Who's ruining our schools?.... The Athiests, that's who.
Why can't I put the Ten Commandments up in courts of law? .... Those damn Athiests.
Etc.
There is even some danger of atheists adopting an offensive posture out of defense against persecution. I've been tempted in this regard. I left facebook recently (in part) due to some hurtful comments by someone (Christian) who I consider to be otherwise a very standup person.
The problem with labels is that they can be dehumanizing. You can attack an "atheist" more easily than you can attack Matt (at least I would hope, on a psychological level).