I agree with you. Currently at odds with the goal of having a society of happy people is the society-wide tendency to attempt to extract value from others. This can make for a lot of very unhappy people who have no resources to reproduce.

Regardless, society is made up of people, and people come from families. The tendencies those families normalize are likely passed down. There are negative tendencies that damage society, and positive tendencies that support society. Working for and with each other is one of those supportive tendencies, and while it can be learned at work or school, kids imprint and learn from their parents the most.

My main point is that if a FIRE couple ends up raising a family but don't have to work for a living, the kids may be missing out on a fundamental aspect of society in their day to day lives. Obviously entitlement is an issue with humans in general, but at a societal level FIRE feels a lot like a selfish "FU, I got mine" and that's not a great tendency to pass down to kids.