I know many religious people who I respect enormously and can recognise that they are better people than me. I also have experienced the positive effects of religious rituals (confession, absolution, communion, religious funerals and weddings, Seder meal, Friday night blessings et al).
I am an atheist because I just can't make God plausible in my mind. Original sin is something I just can't believe in, and if you take original sin out of it, a lot of the theological structure of Christianity gets very weak. Reading the Torah and the Bible properly is also a very chilling experience. Very different aspects of God described in different books, and in the end it comes to seem like a patchwork of different human experiences given a single name - well in fact, given several different names but leave that aside. I admire that I have listened to many sermons trying to explain the Abraham/sacrifice/Isaac story because if I were running a religion I would have made that the first 'lost' scripture. Along with all the other ones. I used to sit there on Friday nights listening to and saying blessings about wanting to be like Rebecca. Then you read what Rebecca was actually like. She's not exactly a role model, put it that way. So did God make her like that? What about Zipporah and her genital mutilation of her son with a flint - i'll say it again, with a flint?
The only conclusion I could live with was that these are humans, behaving the way humans do, and you try to do the best you can and to encourage the best in others. If you start thinking God is involved, the bitterness and pain becomes too much.