From Stewart Brand of The Whole Earth Catalogue comes How Slums Can Save the Planet, an argument for the maximum density and subsequent efficiency that drives all slums (or that slums encourage—this is a chicken and egg issue).
Obviously, the gist is not that we should all convert to slum life. But Brand imagines certain aspects of it (the density, the upcycling, the walkability) can combine with bright green technologies to make urban centres more liveable and sustainable. The article references others that go deeper into the subject, but Brand's piece might be a good fit for anyone with friends or even students curious about contemporary thought on what the future of cities might look like.
Image Credit: Belo Horizonte