I usually roll my eyes at most discussions of the evils of gentrification, especially when the people doing the discussing are relatively new residents of the neighborhood in question. I'm not for any kind of deliberate "slum clearing" policies, and very fast gentrification does, at times, lead to the kind of displacement people worry about. But it's very often a greatly overstated problem, concern for "the poor" by people who generally aren't too concerned with the poor.
But Spike Lee does have at least one very good point here, to the extent that it's true (and I have no doubt that these kinds of complaints are frequently true). Public services shouldn't improve when the neighborhood gets richer, but somehow they do.