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.