It's actually against several of the main religions to do that.
Heh, lots of non-religious people can be worse with thinking that. Whats-his-face spend over a billion dollars on bluntly saying 'Religious people are idiots/wrong. Enjoy life, there's nothing else' in the UK.
I'd suggest not making assumptions until you actually see a questionable post. Seriously. Because assuming as such only makes you just as bad, and could put you in a tight spot.
Sucks that the people around you are like that, though.