Think about this: How long is the new-to-trashed cycle for phones? for cars? for homes? The answers are, approximately: 4 years, 16 years and 100 years.

The problem with your top-down utopian "we shall raze and rebuild our cities" rhetoric is that it always crashes against the massive inertia of the existing built-up landscape. No to mention that people genuinely like their houses, but we don't even need to bring that up.