Tbh I think its more that high IQ people understand the money drain that children are and would rather have around 2 kids than 7.
And that low IQ people would either have more kids for the payout, then realise their mistake later, or just not use condoms.
I don't know, the way I see it is why bring kids into a world you know is utterly horrible? I mean, you've had decades to realize that. Plus, you'll be (indirectly) responsible for all the bad things that happen to them and all the bad things they themselves do. Sure, you'll also be responsible for all the good things too but if the good outweighed the bad, the world wouldn't be all that horrible to begin with. (Sorry, I hope I don't depress anyone)
And that low IQ people would either have more kids for the payout, then realise their mistake later, or just not use condoms.