President Obama reached the wrong conclusion on the controversy between the police officer and the professor.

He said both people overreacted, and by bringing them to the White House for beers, he sought to make the controversy go away.

Instead, as someone who has sworn an oath to uphold the Constitution, he should have taken an unequivocal stand for free speech.

Citizens in this United States have the right to talk back to the police. The cops are not the Gestapo. We should not conclude from this incident that we need to be more servile. Instead, we should conclude that police abuse their authority when they slap a “disturbing the peace” or “disorderly conduct” charge on someone who is standing up for his rights.

In my experience, the mere assertion of one’s rights to a police officer is usually taken by them as a challenge to their authority. It gets their backs up. Especially if the person making the challenge or, “mouthing off,” is a racial minority or a poor white.

Most blacks, browns and poor whites who come in contact with the police have to calculate their situation and modulate their manner, lest they risk arrest, brutalization or even death.

Sean Bell and Oscar Grant are just two of the most familiar victims who received the death penalty at the hands of cops for essentially the crime of being black.

If a citizen asserts his or her constitutional rights, or questions what an officer is doing or speaks in a tone the officer finds unacceptable, this often leads to a charge of disturbing the peace or disorderly conduct. These are catch-all charges that police pin on citizens who refuse to debase themselves with a “yes, sir, whatever you say, sir.”

Many black and brown kids that end up going through the revolving door of the criminal justice system are ushered into it by a disorderly conduct arrest.

What’s more, some cops lie.

Detective Mark Fuhrman in the O.J. Simpson case blatantly lied when he said he hadn’t used the “N” word in a decade.

On November 2, 2006, police in Atlanta killed a 92-year-old black woman named Kathryn Johnston in her own home and then planted evidence and lied about the circumstances. An ensuing investigation revealed many instances of lying and fabricating evidence by police officers.

In the Cambridge incident, Officer James Crowley said in his police report that he talked to witness Lucia Whalen soon after he arrived at the home of Professor Henry Louis Gates. “She went on to tell me that she observed what appeared to be two black males with backpacks on the porch.” Whalen’s attorney said her client never mentioned the men's race to Crowley.

Officer Crowley also wrote that Gates told him, “I’ll speak with your mama outside.” Gates says that the word “mama” didn’t come out of his mouth.

If you believe Whalen, Crowley lied on his report. If you believe Gates, Crowley lied using a stereotypical “black folk talking” buzzword.

The “teachable moment” in the dust up ought to have been a vigorous lesson on our rights, and on how the law is supposed to protect the principle that a person’s home is his or her castle.

Some police have the mistaken belief that they are “the law.” They are not. The law is the law. It’s their job to enforce it.

A person with a badge and a gun and the power to hurt, imprison or kill does not lend legitimacy to our legal system. What lends legitimacy is our belief that the police are dutiful servants of the people — not their arbitrary oppressors.

We, as citizens of a democracy, need to affirm this lesson. We should never have to fear when we stand up for our rights.

Kevin Alexander Gray is the author of “Waiting for Lightning to Strike: The Fundamentals of Black Politics.” He is also a past president of the American Civil Liberties Union of South Carolina. He can be reached at pmproj [at] progressive [dot] org.