Why is it that the leading figures in New Urbanist city planning are people who live in detached homes? What's with their disregard for the less fortunate? Don't the underprivileged also have a right to play loud music and have loud sex?

Everything goes hand in hand. As one of my planning professors told me in college: "It's not the minimum lot size that matters, it's the motion of the single-occupancy vehicular traffic." Thank god she told me that. Before then, I had a serious complex over density requirements.