I guess I could see that angle. Whether I agreed with it would be another story.
I don’t agree with using disease-prevention to reduce population, either. However, there is an observable correlation between lower infant/child mortality and lower overall birthrate. If that is what Bill Gates is pursuing ... then it is.
I don’t see having children as an economic calculation, but then I’m fortunate enough to live in the best country in the world (and have a husband with a great marketable skill, partially due to my effort). It’s an interesting fact that fertility rates among Mexicans in the United States are higher than fertility rates in Mexico ... because you can life decently here with a large family much more easily than you can in Mexico.