Negatives acknowledged, there are huge efficiency upsides to dense human living. Everything becomes smoother, faster, less wasteful. You get a society that leverages economies of scale for everything.
We could also fit more people in if you crushed everyone, dehydrated them and stored they remains in huge compressed cubes. Efficiency is not all we want
In some areas, density is appropriate, and in some areas it's not. I wish we could talk about housing density and "build more housing" as if there was not one universal solution that worked everywhere and for everyone. Dense urban living is not appropriate in a rural or suburban town. Single family homes are not appropriate in a high-demand urban area. Different people want different things, too. No matter how efficient and good for the environment it is, I don't want to live in a concrete honeycomb in the middle of a loud city.