I experimented with various religions in my teens, but I decided to stick with being an atheist in the end. I think if you have a good moral compass of your own that helps you to be good to others or to take care of this world, you don't need religion. It's up to everyone to believe whatever they believe, as long as they have a good working sense of right and wrong. But what scares me about religion is how people try to force their beliefs upon other people and try to tell other what to do and what not to do. Especially when religion gets involved into politics and all decision get based on 'but my God/religious writing says this' only. Over the years and over the time that I met various extremely religious people, I'm sorry to say that I started to associate religion with losing my freedom. I'm okay with moderately religious people who don't try to force their religion upon me. But I've had a little too much strictly religious people tell me I couldn't do things and when I asked why, all they said was 'The Bible says so!' or 'God wants it this way!' (most of them were christians BTW). It's like many strictly religious people only base their views on their religious books and not on anything in the real world and the thought that they'd become powerful enough to rule governments scares me. It's like I'd tell other people what to do based on, let's say, '50 shades of grey' and try to rule an entire country based on the things that were written in '50 shades of grey'. So those would be my problems with religion: that strictly religious people only live by the rules of a book, instead of by common sense or realistic moral guidelines, and that strictly religious people try to tell others what to do and what not to do.
Anyways, my theory on religion is that the first religions were started to explain things people couldn't understand at that time, but at some point some people decided to use religion to tell other what to do and how to live and pretty much control their lives.