In the modern context, if you impregnate someone without planning it out properly, there's a non-negligible chance they'll get an abortion, which is even worse for gene propagation. Furthermore, parents are to some extent legally responsible for their children's actions, so having too many poorly-regulated kids running around means exposing yourself to liability. A big part of the optimal strategy for present-day long-term reproductive success is to get rich, and a big part of getting rich is not having more kids than you can keep track of.

But some people consciously choose never to have any kids. That's silly from the perspective of gene propagation if anything is.