But, lots of people have many kids thst they don't take care of. Genghis Khan is one such example, apocryphally having so many kids as to constitute 2% of the current Asian population having had him as an ancestor. So I don't quite get your point, there is no maximum.
The suggestion falls apart under any scrutiny, you can't force anyone to take care of their kids, if they want to, they will, and if they don't, they won't. Genghis Khan is more closer to our current ruleset than anyone currently is to this suggested rule set, he didn't set any rules, he was following the same rules as people currently do, as I mentioned in the previous sentence.
> The suggestion falls apart under any scrutiny, you can't force anyone to take care of their kids, if they want to, they will, and if they don't, they won't.
I can easily imagine a punishment of forced sterilisation for non-compliance. It wouldn't be the first time human society had that as a punishment.
Also, one of the main things that made it stop wasn't specifically democracy, but that eugenics became unacceptable, otherwise you'd have to explain why you think the US wasn't democratic until 1942: https://en.wikipedia.org/wiki/Skinner_v._Oklahoma