The point isn't that cars aren't useful. The point is we shouldn't optimise for cars. People's individual choices are a poor guide for transport policy decisions. See Braess's paradox, and Downs-Thomson paradox (neither of which are actual paradoxes, just a noting of how individual rational decisions result in a net reduction in utility for all, including the individual).
It's not self-evident to me that we shouldn't optimize for cars. Again, global urban density has been falling for decades, and is likely to keep falling for decades further. There are many, many reasons for this, but at least one of them is that when push comes to shove, many people decide that owning a car is a worthwhile investment, and that additional mobility allows them to live further out. In order to nudge more people into forgoing car ownership, you would need to make cars less useful and less worthwhile, because as long as that advantage is present, people will want them, utilize them, and demand infrastructure for them.
