I can certainly see that your turning point is very valid but I just wonder at the speed of it.
Could NYC have fallen from a reasonably civilised city (not to put on rose-tinted spectacles, we know from gangster movies of the twenties and thirties that the place could be rough at times) to the squalor of Fort Apache the Bronx, Kojak and Death Wish in such a short time? The changes you point to have wrought untold damage but they took generations to reveal themselves.
I’m wondering what is behind the sudden change in NYC from a working city, ie made up of working, ordinary people (even the homeless guys look like they’d take a job if offered) to today’s city made up of deadbeats, welfare bums and super rich.
When did the working classes start leaving the city?
Mid 1950s. Levittown was finished in 1951.
It cleaned up just as quickly when Guiliani became mayor. It was still dangerous and mighty grimy in 1988. By 1995 things had turned 180 degrees for the better.