Hundreds of thousands would live on a street that now houses a thousand people.
I don’t think that density is coming back or desirable.
No one is saying the tenements were desirable, or wishes for them to come back. What we want is the construction of more dense residential housing that can meet or exceed that population density while providing good quality of life. Said construction is entirely possible, doable, and profitable, except that zoning prohibits it in most places.
to save anyone else a search.
> I don’t think that density is coming back or desirable.
I think there's plenty of examples of dense cities (certainly far denser than most US cities) that aren't full of death-trap tenements and it's borderline intellectually dishonest to equate density with that.
In fact, letting NIMBYs have free rein to obstruct/delay/interdict housing construction is far more likely to cause overcrowded/unsafe living situations (which include homelessness) than the other way around.
But on housing, there's a major issue you're not considering. This [1] is a list of US city populations in 1950. This [2] is the list for 1960. So we're looking at the sweet spot of the housing boom and a period where the population also dramatically grew increasing by about 30 million (~20%) in those 10 years. Now you might notice something funny. Nearly every major city shrank in size!
The housing boom did not involve building up (rather literally as is the desire of some people today) in desirable areas so everybody could affordably live there. Instead people sacrificed some comfort and moved outside of cities and started building houses in uninhabited areas outside of the cities. Houses were cheap because people were developing in areas where there was nothing and that nobody wanted before. In turn this movement away from city centers helped keep those prices within the city reasonable, as it had a depressing effect on demand.
The reason prices are so high today is because of simple market dynamics. People are less willing to live in less desirable areas. This is driving the prices in desirable areas into crazy land. There is still immense cheap housing available outside of these areas. Some cities are so hungry for new citizens that they're literally even giving away land on the condition that you put or build a house on it.
Unrelated, a huge point I'd like to see addressed more is how housing costs have outgrown inflation over the course of decades. We used to build enough housing, but NIMBYism and restrictive zoning has taken over recently. Housing is much more expensive in big cities in real terms than it was then, even though fewer people live in them in many cases now (e.g. the population of Manhattan reached its peak in the 1910 census and is down 30% since then). Real wages haven't decreased since the middle-class heydays of the 60s, and a lot of consumers goods have gotten much, much cheaper since then in real terms. The real headwinds in the face of middle-class prosperity are housing costs, healthcare costs, and (to end the digression) university costs, all of which have grown well above inflation.