The point they're making is that the only possible solution is to solve the land use problem, so that the majority of people can live lives that don't require individual automobiles. Broadly speaking, this means building densely enough that walking, biking, and mass transit are suitable for most trips.
I disagree, I think the politics of land use are more easily solvable than the simple physics problem of too many cars, not enough space. Plenty of other countries in the world (and even some US cities) have solved the land use problem to the point that most people don't use space-inefficient private vehicles to get around. It's solvable and there are working models to emulate. This is not true of your alternative.
