I have noticed that atheists don't seem to propagate with as much intensity as the religious do. In fact, in my personal experience (with which I do not intend to judge the entire atheist community) most atheists explicitly wish to have no kids at all. This has nothing to do with their atheism, of course, but with other things that go along with a rational view of life.
Since I am prone to find causal relationships where they don't exist, I have to wonder if there is something that connects the two. In other words, if someone is prone to think rationally and discard or rebuff a faith or religion, does that rational thinking also cause him or her to have less interest in raising a family?
I know that there is an actual imperative in the Bible to 'be fruitful and multiply.' Some Christians simply see this as a command that they should follow. But I don't think that this is responsible for all, or even most, of the joyful childbearing that goes on in the world. Some people really like kids. Some people also really like sex and see children as a natural and, importantly, unavoidable byproduct of sex because they are morally opposed to contraception.
All of that aside, there is a real culture of family in religious circles that I find curiously absent in atheist circles. And this does not mean that atheists do not or should not have children, because they do. But they seem to have small families. Why is that?
For my part, I want no children at all. I like kids. I really do. I think I see the attraction of having a family, but stronger than that is the desire to keep my time to myself. I have a wife, a job and two dogs. I am more materialistic than I think I should be, but having children is not really a good way to overcome that obstacle. In short, I am too selfish to want kids. I like my time, and I like my money. I like my things. And without any kind of moral reason to have kids, I can see no reason why I should. Before I met my wife - who also does not want kids, and came to this conclusion on her own, without my input - I had assumed that I would have kids. This did not bother me, but I considered it to be relatively inevitable. Becoming atheist did not have any particular influence on my desire to go through life childless. I do think, however, that being atheist makes it far easier to come to that decision.
My conclusion is that I am not particularly special or unique. There are plenty of people who have no real reason to have kids. Most such people, however, are under the impression - either vague or explicit - that they should have kids. And I think that this is where neglectful and emotionally abusive parents come from. People who didn't really want kinds but had them anyway, because not having kids is a mark of shame, guilt or a general social blunder. This is another strike of harm that religion causes, albeit an indirect one.