I think that the values of the underclass became the values of the mainstream.
Root causes may have something to do with class, but I would be more inclined to think self-discipline a central issue. I see generations that build up good names and/or good estates followed by generations that simply squander those attainments. A defining difference in those comparisons is self-discipline.
Straining to be non-judgmental sort of seems to erode the ability to develop healthy self-discipline. Indulgence of one generation for the sloppy morals of a following generation handicaps the younger ones, puts them on a path to no defining achievement. I suspect there are cycles, but don't know how to get that perspective.