The most convincing explanation I have heard for these problems is that inner cities massively overconcentrate lead, which is neurotoxic and causes crime/impulsivity. This is a highly solvable problem. But solving it would require us to say things like "the population of inner cities is neurologically disturbed", which would require discussing the problem, which is something that we have to prevent people from doing in order to discourage scientific racism.

The lead-crime link was brought to public attention by a prominent liberal journalist, writing in a prominent liberal/progressive magazine. As far as I'm aware, there was no huge outcry about this. In fact, the article was widely linked and praised in the liberal blogosphere. I am pretty sure that Drum and the editors at Mother Jones would denounce scientific racism quite vigorously if asked about it. So I think you are overestimating the "chilling effect" produced by a taboo against scientific racism.