The neighborhoods that "changed" were largely inhabited by parochial white Catholics, who would freak if they saw a black walking down their block, let alone buying a home. Now the non -religious yuppies are buying in Williamsburg, Bushwick, East Harlem, etc., indicating that those "soft yuppies" are made of tougher stuff than the white Catholics who "tawked like dis."
Oh Clemenza, it wasn't just the Catholics. It was almost anyone who considered himself "White". That's why the suburbs grew as fast as they did. That and rent control with no decent new affordable apartments being built. The old ones not being maintained in order to squeeze the last dime out of them before they imploded.
Actually, having lived in some of the places from which Catholics had been displaced, I can tell you that they didn't get the support that the yuppies got. They were considered Neanderthal grunts by the press and some even ended up in jail for protecting their property and their families. The others eventually left.
The yuppies came in later, when many of the old-timers (both black and white) had left the neighborhood or died and there were many vacant properties. Actually, the first group that came in to these neighborhoods were artists and others looking for cheap space in which they could do whatever they wanted to do. When the place was then gentrified, the yuppies began to move in,with the full support of the press and the city government, which is something the Catholic ethnics never had.
My brother lived in Alphabetland with his artist friends for years, carrying a gun in a brown paper bag everywhere he went. Now one bedroom walkups in his neighborhood are renting for thousands of dollars a month.