This kind of thing becomes a self-fulfilling prophecy when all the poor people get crammed into one place.

Singapore does it right by having high quality housing which happens to have a certain amount subsidized for lower income people. You get a mix of incomes and not a slum.

A lot of California's housing development also incentivizes this type of arrangement: permitting can be fast-tracked and local NIMBYs can be steamrolled if a development allocates some, but not all, of the development to be designated as affordable.