Just before Christmas, hundreds of nonviolent protesters organized by the group Black Lives Matter rallied at the Mall of America. Before the protest, mall officials had told the group they were not welcome. Now, Bloomington City Attorney Sandra Johnson has charged 10 of the organizers with multiple misdemeanors. It’s an unwise use of discretion, which is the core power of prosecutors. Where that great power is used in favor of the powerful against those who are not, it is almost always a mistake.

At any rate, Johnson’s timing is remarkably bad. She has decided to bring charges just as Martin Luther King Jr. Day approaches, and as people are going to see the film “Selma.” That MLK biopic retells a story of nonviolent black protesters who face law enforcement overreaction when they stage a protest after being told not to do so.

The movie also illustrates something that Johnson should take note of: That protesters seek to bring attention to a cause, and that those in law enforcement help them do that when they overreact. Charges not only extend the narrative but bring new opportunities to be heard. Without jail, there would have been no “Letter From Birmingham Jail.”

Prosecutors can’t and don’t charge every possible offense. They define their legacies by what interests they choose to protect. At its best, this power is used to protect women against rapists, to protect the public against armed robbers or to protect future victims against those who would kill. Even at the level of a city attorney’s discretion, there are cases that pose a real threat to something more than convenience in shopping. Protecting a mall from nonviolent protest should be pretty far down the priority list.

Here, the city attorney has two competing parties with an interest in the case: the Mall of America and the protesters. Certainly, the mall is a much more powerful institution, especially as a key taxpayer in the city of Bloomington. The protest organizers are hardly in the same league; one of the 10 is an 18-year-old. By doing the bidding of the powerful mall in doggedly pursuing protesters, the city attorney is protecting an entity that can fend for itself just fine. The people who need the protection of a prosecutor are those who cannot.

I wasn’t at the protest, and I am not part of Black Lives Matter. In fact, I have never been to a protest like the one that was held at the Mall of America. That’s not what I do. However, I am a former prosecutor who trains future prosecutors, and I care deeply about the proper role of law enforcement as protector. There is some irony in prosecutorial overreach against protesters upset about police violence; both are branches of the same wrong.

In the end, that wrong is this: Prosecutors should not press charges and seek restitution against protesters because they can, just as police officers shouldn’t shoot people or apply chokeholds because they can. In either case, these exertions of government power should be used only when necessary, when no other option is available and a greater harm looms. When the government casually uses its power over citizens to shoot them several times, or choke them until they die, or press them for money to pay the police who infiltrate their groups and come arrest them, it has gone too far.

One of the things that Johnson seeks is restitution for the cost of policing the protest. This is an unusual step, and an unfortunate one. Part of what police do, after all, is show up when things are tense. If, say, the University of Minnesota wins an out-of-town championship, the police are going to send officers to monitor the campus and Dinkytown. Sometimes students get unruly, and sometimes they don’t. The police don’t bill the university for what was spent to control the crowds celebrating into the night, even if the university played a role in bringing them together. Do we really want to start parsing out the costs of police doing the job assigned them?

I imagine that there will be a boycott against the Mall of America; there should be. And even though I’m not one who joins a march or chants a slogan, I will shop somewhere else. Sandra Johnson is wrong, and wrong in an important way: She is using a great power simply to aid the powerful.

She may end up in a movie someday, but she probably won’t like it. History is like that.

Mark Osler is a professor of law at the University of St. Thomas.