Why can't Athiests and Christians respect each others personal beliefs?

I'm an atheist, so obviously I think religion is pretty stupid, but I won't go up to a religious person unprovoked and say that. I don't necessarily respect religion, but I tolerate it as long as the person isn't harming anyone or forcing their beliefs on other people. I only get mad when religious people do that sort of thing, and at that point it's not because they're religious, it's because they're being pretty stupid.