The final outcome involves people choosing to reproduce less, obviously. The means to get there in a way that's broadly acceptable is the tough problem. But perhaps not the same order of tough as AI.

• Many religions are hostile to family planning and no mainstream ones I know of are actively in favor of it.

• People who choose to have large numbers of children have the advantage of numbers (insofar that their large-family values get passed onto their children).

• Civil libertarians are uncomfortable with population control because of it being a cover for racist policies in the recent past.

• Economic libertarians are uncomfortable with population control because they have come to associate that goal with intrusive government policy and this prevents them from even considering free-market means to achieve that goal.

• Many, maybe most people like to leave the option of having more-than-replacement levels of children for emotional reasons that were perhaps shaped by evolution.

It's a lot to overcome. Perhaps the first step is at least separating the actual issue from misguided solutions that have been attempted and make it less taboo of a topic for public debate. I don't know, though. It's easier to see the destination than how to get there.