[eru]

Singapore is doing fine at high population density.

[sjwright]

Singapore doesn't exist in a vacuum. An enormous amount of foreign low population density agricultural land is sustaining their lifestyles.

[s_dev]

Singapore is very developed. Overpopulation is more a problem for densely populated developing places - Bangladesh, Victorian London, South American shanty towns et cetera.

[eru]

Yes. Though they only developed in the last 50 years.