Another way of saying this is that because physical space in the city is a scarce resource, the allocation of infrastructure for cars and infrastructure for people is a zero sum game.
Of course, the other thing people in this community may look over is that suburbs are often a fallback when you can't afford a dense urban area. I'm in an LA suburb and renting in LA would be over twice as expensive if I moved down there. Even if downtown LA became walkable, most of the LA county wouldn't be able to afford that living.