Richest and most educated =/= "smartest" and "fittest."
Even your estimation of "fittest" is totally subjective. From a natural selection perspective, the ones with more reproductive success are the fitter ones. And it's not at all established that people with high socio-economic status are genetically smarter or better on any level than low SES individuals. It's more likely to be nurture and access to resources and parenting styles that set them up for success.
Such economies typically have strong public education, fair hiring practices, low barriers to entrepreneurship, and a strong social safety net.
The US had such an economy in the post WWII years, but economic mobility has dropped in recent years. (Probably because we gutted the educational system, and bankrupt people that get sick. Also, WWII trained an unprecedented number of mechanics and engineers in the US.)
Even then you're just assessing how well people fit into a routinized public education system or in a traditional office environment. It privileges a very specific type of skill set at the expense of many others.
The unfortunate aspect of some smart people is that we lack the wisdom to understand that the theories we fall in love with are just shadows of the reality. Even when ideas at their extreme fail we stick to them as if they are an appendix; e.g. capitalism in the extreme even after it has robbed us of meaning, communism even after it caused large-scale hunger and suffering wherever it was implemented.
The problem with the anti-human "environmental" attitude is that it misses the forest for the trees by viewing people as foreign elements in the biosphere. It is as such a theory that anyone but some smart people can spot as unadaptive to reality.
A lot of this seems driven by economics and culture (two incomes are necessary for modern lifestyle; rewards of employment vs home are high (in financial and psychological terms); career, particularly earlier career in the more competitive tracks, is very difficult to juggle with being a parent, particularly for women). Some of this might be addressable (better childcare and child-friendly policies at top employers, especially for junior employees), but a lot of it isn't.
I think there's something worse about differential population growth rates across countries/cultures than a simple across-the-board reduction, but I don't think this is the best environment for that discussion.