> There's a perception, somewhat warranted, that if they can't persuade other people to adopt their preferences, it's going to be harder
Sometimes it is true. Imagine you wish something like the Spanish town model: a very dense centre, and nothing else than the centre, so wherever you are in the town, you just walk/cycle/drive less than a mile and you are in the fields, the hills, or other forms of 'nature'. Density located in a single point would also enable easy and efficient point-to-point public transit between similar towns, by the way.
Anyway, you can't have this if you take the French route and allow suburban sprawl. It will spread 5 miles around in all (free) directions. Then it doesn't matter if you densify the centre (following the mantra "density is good and efficient" which we hear all the time here), people living in the centre (and most of the suburb) will not have access to 'nature' unless they use a car.
(What actually happens in terms of densification in France is generally worse, because densification of the sprawl is not made in the US style with huge buildings in a very dense, punctual, centre, but it is made along some axes or in some areas here and there. You end up with some average density everywhere, while the infrastructure hasn't followed. And cannot follow, because the density itself is spread, instead of being in a single point easily served. The elected from those areas say they want to combat sprawl, but they make it worse for everyone this way.)
On the other hand, I agree that cities, or urbanism in general, shouldn't be designed for what I call the 14-28, like it is often asked on this site. Or at least it should be the only goal and it shouldn't be the goal everywhere. What I mean by 14-28 is people who are in a great demand of interactions, who want to meet people, a lot of people (of course it depends on individuals, I just arbitrarily peeked those figures). It has always been like that, teens and young adults have always wanted to leave and discover the world, to multiply experiences, good and bad ones, and are attracted by the city lights. That's something we must acknowledge, and we'd better provide an environment for that.
BUT that must not be the end of all things. When people get a bit older and become parents, most of them
tone down and wish to be in less hectic areas, that's just a fact we can observe, even if it doesn't match our own ideal. And that's like it until their death, you can find a few people who will move to a city for their retirement but most who move will move the other way. Same for kids: until a certain age, they are satisfied with the presence of their parents, schools, and a handful of neighbouring kids, they have no need or desire of a large and dense city.
So most of their life, people don't care for having a big concentration of people where they live, and on the contrary favour a bit more space and a bit more quietness. Urbanism shouldn't blindly optimise for the former (density).