Why do religious people get so upset about atheists?

I'm not obnoxious about it and don't go around telling people they are wrong. That would piss off anyone. I don't try to logic with people.

But some people get SO UPSET when they learn Im an atheist. I get people trying to convert me, people who are offended by the idea, people who literally cry about my soul, people asking why I have morals then and don't eat babies.

They get more upset when I explain that I've always been an atheist. My parents didn't push religion on me, so by the time I understood what religious was, it sounded absolutely insane to me, and the biblical stories describe god who is angry and vengeful. It never sounded like anything but stories to me.

Im a happy, chatty, gregarious person, and it's like it makes people unhappy that I'm not some sort of lapsed person. They seem to want me to believe in god and I just don't. I see no reason to and no compelling evidence.

I completely understand religion, and it's role in our lives and our world. I see the anthropological purpose it has served humanity. But I don't understand why the idea that I personally believe god does not exist upsets people so much. Its not like my belief would change anything for them. If I'm wrong, I'm wrong. I know people can be really obnoxious about atheism, but I am not at all. I don't think it's stupid to believe, and if it gets your through the day happy, great. Why is my non faith offensive?