In his new book, the Canadian journalist Doug Saunders contends that shantytowns and slums - or arrival cities as he calls them - are necessary for the development of humanity.
Saunders researched Arrival City by interviewing the inhabitants of slums in both the old and developing worlds, and concludes that most ghettos are hotbeds of optimism and entrepreneurship.
With around three billion rural dwellers likely to become urbanised by 2050, Saunders predicts that 40 per cent of these migrants will achieve a middle class income within 10 years and also that the world's population will stabilise, as financial expediency and education naturally reduce the size of families.
But Saunders' perpetually rose-tinted view of the arrival city is, perhaps, the book's major flaw.
He skates over the undoubted misery and degradation that living cheek by jowl with thousands of others in ramshackle accommodation can bring. Nevertheless, he presents a carefully constructed, thought-provoking argument and a hopeful vision of the future.