A con by whom? Obviously, you may not enjoy living close to other people and will choose to live in lower density areas. Fair enough, and, at least in the US, we're not short on space. (I will only add that density is typically measured as people per square foot of ground, meaning you might simply be above and below your neighbors). But creating environments where people can live in higher densities can't be a bad thing.

And the benefits are manifold for those who do want to live in cities. Diversity of options is a big one--that food truck that serves gluten-free venison tacos can only exist somewhere with enough people that such a niche can survive, so the long tail of preferences can be accommodated. Infrastructure is in dense places is cheaper per capita; tearing up one road/pipe/sewer can benefit thousands of people instead of just whoever lives in that one cul-de-sac. Public transportation becomes more practical, enabling people to go where they want cheaper and more easily. A higher concentration of jobs and workers means there can be a better matching of needs and skills, making businesses more successful and workers happier.

So sure, you may wish to forgo all that to have a yard and some space. I'm sure the housing market and broadband companies will oblige. But in general, practical dense cities will be a boon to society, from which we'll all benefit.

Edit: clarity.

Not only all that, but there's been a lot of evidence over the past couple of decades that the rate of innovation per capita goes up with density. Density brings more people into contact more frequently, which leads to more innovation, more economic growth and more employment.

Is that still true though? (genuine question).

When I was a boy, twenty years ago I firmly believed that I would need to move to London as soon as I could, just for the British library and access to information. Then the internet happened (well the web, and it was already happening but for me, that's when it happened). The internet made distance so much less of a factor, and i suspect that this trend will only continue. I suspect the density/creativity association will break down, but I have no evidence either way, so I could be completely wrong.

Still true. If anything, it's getting more true over time as cities get more efficient at bringing people into productive contact.

lots of roads can be one lane one way if all the drivers are perfect.