Also, economic progress reduces fertility rates dramatically, so that most of the first world is below replacement levels.

The sex ratio problem can potentially lead to a lot of violence. The idea that a significant proportion of young males will never have a mate creates natural aggression, which may be useful to a state like China if it can control it, but in general seems like a really bad idea.

Even when there is no enforced population control, the sex ratios are starting to swing in those cultures which place much greater value on males than females, such as India. One wonders how the Muslim countries do in that regard... or do they prohibit abortion?

"the destruction wrought by modernity on organically developed indigenous cultures is quite often a good thing."

Here in Arizona this destruction is currently in a very negative stage. Although members of the Native American culture who assimilate ("urban Indians") have no problem, those on the reservation suffer from an abundance of social ills. This was true when they were all poverty stricken, and is still true now that many are wealthy from their casinos. The highest violent crime rate in the Phoenix metropolitan area is on two adjoining Indian reservations.

A relative teaches at a remote reservation in New Mexico, where poverty is rampant and few non-tribe members are closer than a 1 hour drive. But that tribe also is disintegrating, with virtually no intact families and many damaged youth.

Personally, as a long-time southwesterner, I would prefer that the special status of Native Americans simply disappear, and the reservation land be divided up among the members. This would accelerate assimilation which would probably end a lot of unhappiness and criminal behavior. The side effect would be the loss of some interesting rituals and art, but those are fading anyway with the current slow and bloody disintegration of the indigenous culture.