I think religious ideas exist because they're propagated in youth, mostly, and then carry over from there depending on how strict of a parent and religious upbringing that person has. I'm sure some people find them accurate, but when pressed for the 'why' they invariably make stuff up. This is not to say Atheists don't do the same thing as I've met a few who do the same thing--that's just a human thing. The trouble, as I've gotten older, is that it's really difficult to justify things with language and to describe why I feel the way I feel. You're trying to put words to thoughts and feelings which are not actually all that rational sometimes. So when pressed for reasons and such it's less of an emotive gut reaction and when people think about these things, their best reasoning often makes no sense because the feelings they're trying to express with words is inadequate to describe that feeling. I tend to disagree that the purpose of a religion isn't to sustain itself and there's plenty of examples with the 'Go forth and multiply' command and the quiverful movement. Now, these things aren't that widespread but the idea is to generally have kids, raise those kids in that faith, and the cycle repeats. Therefore on the whole the 'good book' is about the nice morals and the being good to everyone, but I tend to view that as window dressing to get followers to feel secure in their faith and less about actually doing those things. I do seriously question if these people believe that religion is an 'accurate explanation for the way the world works' or if they're just following repeated patterns that they've grown accustomed to from their youth and it's just....a philosophical inertia.