Density also comes with it's own problems - crime, pollution, disease, and a loss in personal freedom necessary to keep those other problems at bay. None of that is ideal for family formation.

And increasing density only works up to a point. Once you can no longer increase density, the prices start climbing back up.

I think rezoning for more mixed use neighborhoods is a good idea, and some high-density living is good (not everyone has kids, or wants to have them) but I am skeptical of increasing density in general.