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Amid the rioting in Milwaukee, there is also a clash between two leading lawmen there -- Milwaukee County Sheriff David Clarke and the city of Milwaukee's Chief of Police Edward Flynn. They have very different opinions about how law enforcement should be carried out.

Chief Edward Flynn expresses the view long prevalent among those who emphasize the social "root causes" of crime, such as income disparities and educational disparities, as well as the larger society's neglect of black communities.

Chief Flynn puts less emphasis on aggressive police action and more on community outreach and gun control.

Sheriff David Clarke represents an opposite tradition, in which the job of the police is to enforce the law, as forcefully as necessary, not to make excuses for law-breaking or to ease up on enforcing the law, in hopes that this will mollify rioters. Sheriff Clarke would also like to see law-abiding blacks be armed.

Differences of opinion on law enforcement are sharp and unmistakable -- and have been for more than 50 years. However, as the late Daniel Patrick Moynihan used to say, "You're entitled to your own opinion, but you're not entitled to your own facts."

Unfortunately, facts seem to play a remarkably small role in clashes over law enforcement policies. And that too has been true for more than 50 years.

In his memoirs, the Supreme Court's Chief Justice Earl Warren declared that "all of us must assume a share of the responsibility" for rising crime rates in the 1960s because "for decades we have swept under the rug" the slum conditions that breed crime.

But the hard fact is that the murder rate in the country as a whole was going down during those very decades when social problems in the slums were supposedly being neglected.

Homicide rates among black males went down by 18 percent in the 1940s and by 22 percent in the 1950s. It was in the 1960s, when the ideas of Chief Justice Warren and others triumphed, that this long decline in homicide rates among black males reversed and skyrocketed by 89 percent, wiping out all the progress of the previous 20 years.

The same reversal in the country at large saw murder rates by 1974 more than twice as high as in 1960. This was after the murder rate had been cut in half from where it had been in the 1930s.

Ghetto riots, which erupted in the 1960s, were blamed on poverty and discrimination. But what were the facts?

Poverty and discrimination were worse in the South than in the rest of the country. But ghetto riots were not nearly as common in the South.

The most deadly ghetto riot of the 1960s occurred in Detroit, where 43 people were killed -- 33 of whom were black. In Detroit at that time, black median family income was 95 percent of white median family income. The unemployment rate among blacks was 3.4 percent and black home ownership was higher in Detroit than in any other major city.

What was different about Detroit was that politicians put the police under orders that restricted their response to riots -- and some rioters said "the fuzz is scared." It was black victims who paid the highest price for letting rioters run amuck.

By contrast, Chicago's 1960s mayor Richard Daley came on television to say that he had ordered his police to "shoot to kill" rioters who started fires. There was outrage among the politically correct across the country. But Chicago, with a larger population than Detroit, had no such death rate in riots.

In later years, New York Mayor Rudolph Giuliani's aggressive police policies in high-crime neighborhoods cut the murder rate down to a fraction of what it had been before.

But, in England, opposite policies prevailed, with what London's "Daily Telegraph" newspaper referred to as "politically correct policing" that has police acting "more like social workers than upholders of law and order."

Although England had long been regarded as one of the most law-abiding nations on Earth, riots that swept through London, Manchester and other British cities in 2011 were virtually identical to riots in Ferguson, Baltimore and other American cities. Most of the British rioters were white but what they did was the same, right down to setting fire to police cars.

But do facts matter anymore?