Perhaps you did read it but you sure as hell didn't understand it. Neither did a lot of other slashtards judging by the flood of idiotic commentary further down.
The author talks about the benefits of high population density at all income levels. City dwellers use less resources than people in rural areas.
No one wants to live in a slum... except the millions of people moving from rural areas into slums every year. They're not all completely ignorant, it's just that the countryside around the city is even more of a hellhole than the slums. Thinking used to be that that wave of migration should be stopped at all costs but that has changed and in many country it's now policy to try and improve the situation in the slums instead. That's because planners have come to realize that by and large urban poverty's better than rural poverty. Education, sanitation, health, social mobility, environmental footprint, cities are superior to villages in almost every way.
I don't know where everyone got the idea that the author recommends that we turn regular cities into slums or that everyone should be poor. 90% of the upvoted comments are variations on "omg he sezs we should all live in slums. the author should try living in one, kthxbye." I haven't seen so many burning strawmen outside a Microsoft article in years.
P.S.: The only valid argument I could find in 10 pages was about transport costs but it still is wrong. Yes, transporting food costs energy. But it's not much. When people talk about local food in rich countries they aren't talking about growing vegetables on your roof. The problem is that vegetables from Virginia are shipped to Thailand for processing and then shipped back to Maryland.