While I'm all for this, the problem I see with high-density buildings is that it's easy to put them up, but it's hard to then build the services that this many people need. You can put an apartment block with hundreds of new residents, sure, but where are the doctors, the schools, the hospitals, the public transport routes, etc?
All very solvable problems, but one that high-density living often fails to cater for, because some rich developer cunt is happy to throw a high rise up and forget the rest.