It is especially bad on fundamentalist Christian message boards on the internet, like the ones that are especially theologically conservative (like oriented to the Rapture) and also the ones that are more politically and socially focused. They just demonize, both literally and metaphorically, us atheists and repeatedly state how self-worshiping and stupid and depraved we are. They do not realize that we are right around them already and they have positive close social interactions with us already, and so would know that those vile claims are just not true. As long as we can be separated out and treated as a remote outsider group off in the distance though, it is easier to sustain those false claims about us.
Brian
These folks have never socialized with atheists or muslims or liberals or whomever they're demonizing. They're racists that need to decondition. Likely they won't, however as they probably lack the a larger intellectual perspective. There's no way you can move around among a diversity of people and continue to hold such prejudices.
Sure, I think believing in invisible sky people is dopey, childish and provincial, but I know and interact with lots of people who do.