The same proportion of white people as black smoke marijuana. So why are the incarceration rates for black dope smokers many times higher?

Why have incarceration rates overall in America quintupled in the past 30 years, while the nation’s crime rate has not changed substantially? And why does this country have the highest imprisonment rates in the world?

Racism, that’s why. The five members of the panel assembled at Edgartown’s Old Whaling Church last evening were unanimous on the point. A racism different in form from those of the past, but every bit as effective in oppressing people of color — primarily African Americans, but also other minorities.

The topic for this year’s forum organized by Henry Louis Gates Jr. for Harvard’s W.E.B DuBois Institute for African and African American Research was Locked Out, Locked Up: Black Men in America. And the panel laid it all out in depressing detail, statistics and anecdotes included.

First up was Michelle Alexander, associate professor of law at Ohio State University, author of The New Jim Crow.

She told the audience she had come to see the American criminal justice system as “the primary vehicle today for the creation and maintenance of racial hierarchy in the United States.

“The mass incarceration of poor people of color has operated to create a caste-like system in which millions of people are locked into a permanent second class status for life, highly reminiscent of what we supposedly left behind.”

The penalty for minor, victimless crime is not just imprisonment, but exclusion from public housing, food stamps, other social welfare, the loss of the right to sit on juries and, importantly, voting rights. And often unemployment, because victims of the system continue to be forced to check the “felon” box on job applications, “whether their felony happened three weeks ago or 30 years ago,” she said.

And while it is no longer acceptable to be overtly racist, she said, “today it is perfectly legal to discriminate against criminals in nearly all the ways that it was once legal to discriminate against African Americans.”

And because African Americans are grossly over-represented among the ranks of the convicted, it serves the same purpose.

Her statistics are compelling: There are today more African Americans under some form of correctional control than were enslaved in 1850. In 2004 there were more blacks denied the right to vote than there were before 1870, when the 15th amendment was ratified.

In Chicago today nearly 80 per cent of men are subject to what she called “legalized discrimination” for rest of their lives. America does not have an underclass, but an undercaste.

Given that violent crime rates have remained constant over the past several decades, she said, the trend in incarceration rates can be explained only in terms of racial politics.

Calling it a backlash against the success of the civil rights movement, Ms. Alexander said the law-and-order rhetoric which has become such a constant part of political discourse, particularly conservative political discourse, can be traced to former segregationsists.

She said it is part of the Republican party’s strategy to attract working class whites away from the Democratic party in the South.

And she said that President Reagan’s war on drugs had “criminalized millions of poor African Americans for drug crimes, committed with equal frequency by whites.”

New York Times columnist Charles Blow next explained how this works, and spread the blame to the Democrats, including the Clinton and Obama administrations.

“The entire police departments of whole cities are in on this racket,” he said. He gave an example of New York, where police resources are concentrated in black neighborhoods, where they can stop and search just about everybody they see.

This resulted in 55 per cent of those arrested being black, while 30-plus per cent plus are Hispanic and 10 per cent are white. In most arrests marijuana possession is the only offense.

Ironically, though, having a joint is not a crime in New York. Being caught with less than seven-eighths of an ounce is punishable with the equivalent of a parking ticket: a fine, no crime, no record

But showing the drugs in public is a crime. So the police will ask suspects to produce any drugs they had, which constitutes showing it and results in a crime and a record. There are 40,000 such cases in the city each year.

Some estimates, Mr. Blow said, put the cost of this policing at $50 million a year. But the federal government pays for it through grant funding. Another irony: the Bush administration was phasing out the grant program, but Barack Obama had made a campaign promise to restore it, and then gave it stimulus money. The program has been quadrupled in size to $2 billion.

President Clinton had signed a law denying financial aid — “No grants, no nothing” — from the federal government to go to college if you have a drug arrest in your past at any point.

“All of a sudden it makes a lot of sense why young black women may be in college and the men are not,” Mr. Blow said.

Lawrence D. Bobo, professor of social sciences at Harvard, said there now are more black men of college age in prison than in college.

But it is not just black people who are victims of America’s “new mass incarceration society,” as he put it. According to Professor Bobo’s statistics, one in 100 Americans is now behind bars. One in 15 black men are either in jail or in prison, and one in nine between the ages of 20 and 24 is in jail or prison.

More than 60 per cent of poorly educated black men are likely to do jail time before age 30.

“The in-state expenditures on jails has far outstripped the growth of all other state expenditures with the exception of Medicaid,” he said.

It dwarfs the rate of growth in spending on higher education. It costs an average of $29,000 a year to keep a prisoner locked up, a total in 2007 of nearly $50 billion, four times what was spent 10 years earlier.

A second New York Times columnist, Bob Herbert, was asked by the panel moderator Charlayne Hunter-Gault what could be done about it. He picked up the question.

“How long do we allow this to go on? How many lives do we have to lose? How many generations walk the plank before something gets done?” he asked.

He also noted that apart from the people imprisoned for crimes that did not deserve imprisonment, there were many imprisoned for crimes they didn’t commit.

“Rogue police officers . . . prosecutorial misconduct. Every kind of abuse you can imagine is out there. I covered a lot of it,” he said.

”We stop and frisk and humiliate over a half-million people a year in New York city. Most of them are young black and Latino men and boys and 90 per cent of them are innocent of any crime at all.”

What is needed, he said, is to reinvigorate the fight for social justice. Government will do nothing until pushed hard.

“What I would like to see is a mobilization — and I think it would have to start with black people — on the scale of the civil rights movement,” he said.