"You'll gradually get more density and less traffic this way over time, assuming that's what people want (and if it's not, they'll get what they want instead)"

"You'll gradually get more density and less traffic this way over time, assuming that's what people want (and if it's not, they'll get what they want instead)" That's not how it works. Aggregate preferences doesn't, necessarily, give you the best of worlds. All kind of local minimums and nasty equilibriums are possible.