Something can be normal in the sense of what typically happens without being reinforced as a cultural norm. As an unrelated example, homosexuality has existed for an extremely long time, so it was “normal” in the sense that it was something common, but it was not culturally accepted as normal in the Western world until much more recently. By reinforcing the cultural norm of making babies, the author lends social acceptance to bringing someone into the world without their consent while simultaneously contributing to all of the environmental problems of human overpopulation.

Of course I’m not trying to argue that reproduction doesn’t happen; I was making the point that it doesn’t need to be considered the default. For many people before the age of puberty, the idea is rather unappealing, and they lose that aversion partly due to social factors.