Thousands of people rallied peacefully in Baltimore last weekend to protest the still-unexplained death of Freddie Gray, who died in police custody under highly suspicious circumstances. In doing so, the protesters acted as civilians ought to do, seeking to hold the city police department and the municipal government accountable for their actions.

Others in Baltimore, however, took advantage of the moment of crisis to resort to violence. They threw rocks, burned cars, looted and destroyed buildings, and generally caused havoc that virtually shut the city down early this week.

Figures on the left have tended to express some sympathy for the rioters, regarding the riots as a kind of extension to the peaceful protest.

President Barack Obama’s reaction was typical: Though he denounced the violence, he argued that riots are the predictable consequence of inequality, injustice and hopelessness. He concluded that, to prevent future riots, the government ought to spend more on social services for the poor.

Further to the left, writers like Benji Hart (writing in Salon) and Ta-Nehisi Coates (in The Atlantic) have rejected the presumption in favor of non-violence and defended the rioters. Coates likens the riots both to forest fire and war. Like forest fires, riots may be seen as basically natural and necessary consequences of injustice; like war, a riot may be seen as an act of violent resistance to oppression. In either case, he suggests, it is wrong to blame the rioters.

Still more radically, Hart endorses violence, or “militance,” as he prefers to call it, as the appropriate response to oppression. “Militance,” he writes, “is about direct action which defends our communities from violence.”

Hart’s theory may hold a certain romantic appeal to people who dream about revolution, but in the real world, it makes no sense. The problem is that the rioters do not defend but rather destroy their own communities. Moreover, if reform of the police department is the political objective, it is counterproductive to prove to your neighbors that, where the police are overwhelmed by crime, life becomes nasty, brutish and violent.

Nor does Obama’s diagnosis fit the facts. Riots sometimes happen in the absence of injustice — for example in cities or on college campuses after the local team wins a sports championship, and they do not invariably happen even after great or spectacular acts of injustice. Nor did Monday’s riots even start at the scene of a protest. The Baltimore Sun reported that they began when students confronted police at a shopping mall, far from protesters.

Moreover, if adopting the Democratic Party’s policy agenda and increasing government spending were going to cure riots, one must wonder why they haven’t already achieved the desired result — especially in Baltimore, Maryland. Baltimore is a deep blue city, having been ruled almost continuously by Democrats for decades, and it is part of Maryland, a deep blue state, with among the highest taxes in the country and very generous social services.

Nor is race part of the equation in Baltimore: the current mayor is black, as was her predecessor; the current police commissioner is also black, and not the first African-American to hold that position. The police force is almost half black in a city that is 60 percent African-American.

A better account of riots is provided by scholars David Haddock and Daniel Polsby, who start from the observation that riots differ from ordinary acts of petty crime in that they involve groups of people who coordinate their crimes to overwhelm the police, so that they can loot and vandalize with impunity. But the coordination is not provided by some organizing person or “outside agitator.” Instead, it takes some triggering event that will prompt crowds of people interested in rioting to come together.

That event may be victory in a sports championship or the occasion of certain kinds of political protest. It doesn’t matter. What matters to the rioters is that a sufficiently large crowd of people eager to do violence be assembled. The riot starts when some in the crowd judge that if they start the violence, the rest likely will join in. Once started, the riot persists as long as the crowd of rioters is large enough and active enough that the police cannot effectively respond to individual crimes.

Baltimore’s police department still needs to explain Freddie Gray’s death, and if wrongdoing is found, the perpetrators need to be punished, his family compensated and the department reformed to prevent such wrongs in the future. But what the rioters deserve, too, is punishment — not sympathy.

Joseph R. Reisert is associate professor of American constitutional law and chairman of the department of government at Colby College in Waterville.