I've not noticed them being angry, but they definitely don't like it.... as former theist myself, I think it's mostly frustration stemming from true belief that you/we are "going to hell" and they really want to "save our souls" by converting us... That's how I felt when I was a theist in my teens - it's mostly genuine empathy and concern. It's all about this "hell" bullshit which is ultimately the primary real actual motivating force which scares people into staying in religion that deep down seem to make zero sense to them (except Islam which uses both that AND actual violence/death meted out by humans for "apostates" and "blasphemers" ).

I think most believers see non-believers as a threat. If they meet an atheist who doesn't fit their stereotype, they get completely hung up and don't know what to do. I think it makes them question themselves. "How can this godless person be so 'normal'???" I think when they realize that we don't all have horns, aren't miserable wretches, aren't trying to make them worship satan, and aren't trying to eat their children, it challenges everything they thought they knew. How can anyone be "good without god"??? I've had people, who didn't know I was an atheist, be completely shocked when learning I am. When they ask how it's possible they didn't know, I tell them that we don't all wear t-shirts so they can pick us out of a crowd, and while they're all in church, we usually do our grocery shopping because the stores are less crowded. Or we're sleeping in because it's Sunday.

I think, "misery loves company" and I also think people feel less cognitive dissonance and comforted when others "believe" what they do.

I havent found that to be the case.

It's fear based. People tend to feel fear when they encounter unfamiliar territory. Most folks don't like exposing their fears, so it is projected as anger.They would be much more comfortable treading in familiar territory.

I think it bothers them that more people are being none believers too

It's insecurity stemming from the accuracy of certain seemingly absurd beliefs that are constantly contradictory to itself as well as reality.

I think there are various reasons, from truly believing that atheists are evil to being insecure in their own belief and feeling like disbelief or non-belief is an affront to their faith.

They are normally around people who agree with them and strengthen their beliefs. Not believing is a kick in the gut, and tends to prey on their doubt, their reason. For many it is actual fear.

Hmm... I think it stems from a personal fear of their own, to die and become nothing more. People tend to fear or be angered by things they don't understand and in that, they cannot fathom how one is able to go through a life without some direction via divination. In a way it poses as a threat to their own beliefs by the mere point of stating such beliefs.

I’ll answer that with another similar question. Why is it that a lot of non-believers seem to be angered by anybody with a religious belief?

Can’t wait for the rationalized distinctions. I’m not judging, because religious people use to anger me all the time too, and still do sometimes, but my level of getting “upset” is now pretty much non-existent. We all need to relax. I understand the frustration with dealing with people whose religious beliefs that seem to be irrational and disrupt the flow of one’s day. But as far the people thinking you or people like you will suffer punishment when you die, they either legitimately care about you and know no other way of expressing themselves, or they are confused with their own belief or lifestyle choices and are scared themselves of what may happen to them when they die or even how people think of them in this life. Just remember that, when you experience people of faith or otherwise. Best thing to do is smile and don’t show your anger or frustration and try your hardest to actually genuinely feel compassion and empathy for others even if they don’t deserve it. I know this sounds cheesy but I really believe this is the best thing to do.

If you were say a Jew, the good Christians would leave you alone. BUT if you have no religion, they have an issue. They think you’re lost or something. Little do most of them know how comfortable I am!

They feel threatened by people who don't believe. We all (probably) harbor doubt about our beliefs, but if you are follower of some religious group/tenet/whatever, doubt is dangerous and people who don't believe are a manifestation of that doubt.

They confuse us with psychopaths... They're ignorant!