I’m a lifelong liberal. I voted for George McGovern, Ted Kennedy, Jerry Brown, and more recently Al Gore, Hillary Clinton and Bernie Sanders. I marched with Occupy, support the Sierra Club, and laughed when Jon Stewart exposed the bias on Fox News.

But I’m also a psychiatrist who has spent 30 years treating addicts and alcoholics, and I know this: There’s nothing Fox News has ever been accused of that the mainstream media isn’t also doing — for marijuana.

Take one example: a lot of people think prisons are filled with inmates whose only crime is drug use, especially marijuana use. It’s not true.

Yes, 20 percent of U.S. prison inmates are incarcerated for drug crimes, but they were almost all selling drugs.

According to research published in Contemporary Drug Problems, only one-half of 1 percent of the U.S. prison population is locked up solely for drug possession. For marijuana, it’s one half of one-tenth of 1 percent — about 400 inmates nationwide. And those numbers are probably high because drug possession is often the lesser charge in a plea deal.

In other words, the odds of going to prison just for smoking weed or carrying coke is practically nil. But our major media outlets keep telling us otherwise.

For example, in an April 2, 2012, Time magazine column titled “Incarceration Nation,” Fareed Zakaria wrote, “…something has happened in the past 30 years to push millions of Americans into prison. That something, of course, is the war on drugs.” No, it’s not. Eighty percent of prison inmates are incarcerated for non-drug crimes. If we repealed every drug law, we’d still have mass incarceration.

In a November 2012 Washington Post column, Katrina vanden Heuvel wrote that legalizing marijuana would “drastically decrease incarceration rates.” However, the research from Contemporary Drug Problems found that only 2 percent of U.S. prison inmates are incarcerated solely for marijuana offenses, almost all of them for trafficking. Two percent is not by any definition a drastic decrease.

A July 28, 2014, New York Times editorial called, “The Injustice of Marijuana Arrests,” told the story of a man in prison for 13 years because of marijuana laws. But it wasn’t marijuana laws. The man received his long sentence because of repeat offender laws. He could just as easily have gotten his “three strikes” for any crime.

This is only federal prison data, but HuffPost labeled it as all prisons. Half of federal prisoners are incarcerated for drug trafficking.

On March 10, 2014, Huffington Post ran a story whose first sentence was, “America’s prisons are dangerously overcrowded, and the war on drugs is mainly to blame.” That’s not true; it’s at most 20 percent to blame. But Huffington Post made it appear true by using a graph of federal prisons — where half of all inmates are drug traffickers — and then mislabeling the graph as inmates from all U.S. prisons.

Of all prison inmates, federal and state, only about 16% are in for drug crimes, almost all for sales.

On July 30, 2015, Politico ran an article called “Congress’ Summer Fling With Marijuana,” that referred to “the high costs of sending millions of people … to prison for nonviolent marijuana offenses…” That’s ridiculously untrue. The United States hasn’t sent a million people to prison for marijuana over its entire 240-year history.

Why does the press repeatedly get this wrong? One possible reason is that blaming the drug war for mass incarceration has become such an article of faith, even for many reporters, that they never question whether it’s true.

A bigger problem, however, is that journalists who use marijuana are allowed to write about it. This is a conflict of interest. One reporter covering the raw milk issue for a big city daily said she was taken off the story when her editor learned she drank raw milk herself.

Marijuana is even more of a problem. The 1970 marijuana user guide A Child’s Garden of Grasssays, “grass smokers are the world’s greatest proselytizers,” and they are. They seem to believe marijuana can do no wrong.

Letting pot-smoking reporters cover the marijuana issue is fox-guarding-the-henhouse foolish. It’s a recipe for biased journalism and a misinformed public. It’s probably why people don’t know that the drug war didn’t cause mass incarceration and that virtually no one goes to prison just for using drugs.

And it’s why my fellow liberals and I should criticize the bias in our own news media and not just Fox News.

This appeared in the Arizona Capitol Times.