George Zimmerman's acquittal of murder charges in a Florida court has been followed by predictable calls for America to have a "national conversation" about this or that aspect of the case. President Obama wants to talk about gun control. Civil-rights leaders want to talk about racial profiling. Others want to discuss how the American criminal justice system supposedly targets black men.

All of which is fine. Just don't expect these conversations to be especially illuminating or honest. Liberals in general, and the black left in particular, like the idea of talking about racial problems, but in practice they typically ignore the most relevant aspects of any such discussion.

Any candid debate on race and criminality in this country would have to start with the fact that blacks commit an astoundingly disproportionate number of crimes. African-Americans constitute about 13% of the population, yet between 1976 and 2005 blacks committed more than half of all murders in the U.S. The black arrest rate for most offenses—including robbery, aggravated assault and property crimes—is typically two to three times their representation in the population. The U.S. criminal-justice system, which currently is headed by one black man (Attorney General Eric Holder) who reports to another (President Obama), is a reflection of this reality, not its cause.

"High rates of black violence in the late twentieth century are a matter of historical fact, not bigoted imagination," wrote the late Harvard Law professor William Stuntz in "The Collapse of American Criminal Justice." "The trends reached their peak not in the land of Jim Crow but in the more civilized North, and not in the age of segregation but in the decades that saw the rise of civil rights for African Americans—and of African American control of city governments."

The left wants to blame these outcomes on racial animus and "the system," but blacks have long been part of running that system. Black crime and incarceration rates spiked in the 1970s and '80s in cities such as Cleveland, Detroit, Chicago and Philadelphia, under black mayors and black police chiefs. Some of the most violent cities in the U.S. today are run by blacks.