I'm actually pretty sure some people who have had 12 kids are heroes or at least very altruistic when objectively analysed.

Many many people that made great contributions have come from large families of overachievers. Genetics and upbringing matter a lot. And productivity gains made by lets say 6 of the kids can easily overshadow anything that one individual could have done (even when adjusted for the fact that the kids start contributing later).

However overall if we look at the world today, the vast majority of people having 12 kids aren't heroes.