The hostility can also be based upon doubt.
Religion is about convincing yourself that God exists. But everyone is fallible and makes mistakes. What if theists have made a mistake about their belief? Going to houses of worship, studying holy books and praying won't make that doubt go away. It remains there because it is impossible to convince yourself to the point of removing all self doubt. In order for that to happen it must be stepped up to the level of brainwashing but that is not a conviction either.
So for theists who are honest with themselves there is always this nagging doubt and their hostility towards atheists stems from seeing their own doubts in the flesh, so to speak. The religion of theists claims that heathens suffer from all kinds of imaginary problems but in the flesh atheists are normal people leading normal lives. They are friendly, funny, open and giving. They care about others, make donations to good causes, volunteer to help the less fortunate and generally lead good lives.
And they doing all of this without any imaginary deity in their lives. They don't pray, congregate or proselytize. They don't pay tithes or claim that gay marriage will bring about the apocalypse.
Hostility towards atheists is not because they don't believe. Hostility towards atheists is because believers have a hard time dealing with their own self doubts when faced with the normality that is everyday atheism in my opinion.
I've often thought the same thing. They're see us as their own doubts staring them in the face. Or in the case of the really deluded ones, they believe that we're utterly hellbound and are afraid that we'll get some of our taint on them and drag them down with us.
The vast majority of theists are normal ordinary folk who probably don't care about atheists or even see them as a threat either. It is only those who do feel threatened who the ones with the most self doubt. Their beliefs are usually in absolutes and don't allow for any gray areas but they are human and still have to deal with themselves. They can't pray away the doubt so instead they turn it into hostility.
In some respects I feel sorry for them. It can't be easy having to convince themselves over and over again, day after day, that things will be better after they are dead. I suspect that is why they want the 2nd coming during their lifetime. They want to be alive to see their doubts dispelled. But since that is never going to happen they actually spend their lives wishing for them to end. How sad is that?
A string of thoughtful comments.
I think the above arguments describing belief in the supernatural can be resolved by identifying one of the various dynamics that motivates religious beliefs: The deep seated fear of dying, fear of the unknown and a desire to experience our lives. Perhaps not everyone shares those feeling, perhaps not everyone can.
There does not need to be religions or gods for there to be a purpose or "meaning" in life. One's purpose in life may be incremental and limited but may be of considerable consequence, both in the present and to posterity.
But the struggle over the questions of our existence have no requirements for angry gods. Pondering all great mysteries is the real thing that sets us above the animals. Perhaps in the end, sentient life is the universe's way of trying to understand itself. But I consider that search for answers a noble struggle it's not the religious entities who are doing the search. I applaud the exploration of life's mysteries and it makes me feel good about the human condition. And, what is more courageous than saying, "I want to know the
truth?" (wherever it leads).