Check out this article on How Race Wrecked Liberalism by James Nuechterlein. [First Things, August/September 2005: Articles]

If you've forgotten the old riots of the Sixties, you might be interested to know some of these things:

Infinitely more troubling to political moderates were the violent racial protests in the North that began in 1964 and continued, in escalating severity, every summer for several years. Within two weeks of passage of the civil-rights legislation of 1964 a major riot broke out in Harlem, followed quickly by outbreaks in other northeastern cities. Just five days after passage of the Voting Rights Act in 1965 came the conflagration in Watts, one of the deadliest race riots in the nation’s history.

It would be difficult to overestimate the damage that those and subsequent riots did to the cause of civil rights. White guilt dissipated; white outrage flourished. Moderates had assumed that in supporting civil-rights legislation they were both doing the right thing and purchasing social order. When that implicit bargain broke down, they felt betrayed, and they became increasingly dubious about arguments that only further legislation would make possible a break in an endless series of “long, hot summers.”

The reaction to the riots on the Left further unsettled moderate whites. King, not surprisingly, blamed specific outbreaks mostly on official misbehavior—often police brutality—and put increasing emphasis on the economic roots of black protest. He called the Watts riot a “class revolt” of the underprivileged. Many white liberals, while insisting that they did not condone black violence, so emphasized the importance of understanding the frustrations leading to its occurrence that they seemed to be justifying it.

And the riots weren't happening in the Jim Crow South, where blacks could complain of genuine oppression; they were happening in places like Los Angeles, where black already enjoyed equal rights, as a matter of California law.