I would not say that dense city living is not without its downsides. But if people need to work in these cities, they may as well get to live closer. And if you are already living in an apartment, it's not that much different to live in a 6 story apartment building vs a 4 story one.

> There would be 3-4X the people, yet still the same amount of roads, services, and public utilities.

That's the point! Per capita, it should be cheaper to live in cities because infrastructure goes so much further. And if you are arguing for better mass transit, you will have to build many, many more miles if you also want to encourage people to sprawl.

Although I think the strongest case for allowing cities to get dense is it allows greenbelts and less dense areas closer to the city. You can build a big dense city UP and make it easier for people to get out and enjoy nature and farms and etc. Or you can build a city OUT and then it's just desolate city for hours around.