I actually have some data from my sociology class that could support his claim. I don't have a reference to give you, except that the story is found in "The Human Experience" reader. I don't have it handy, or I'd give you a more exact reference, but the gist of the article was that all victimless crimes - not just marijuana, but also things like prostitution - serve to keep peoples' eyes off of the rich. It's typically the poor who are driven by desperation to do many of the victimless crimes (though, I suppose that could be argued in the case of marijuana, but there's still a significant portion of marijuana smokers who are poor or middle class).
In essence, when someone is arrested for marijuana or another victimless crime, it goes on their permanent record. It keeps the poor poor, because these people find it difficult if not impossible to find a steady job with a criminal record, and so, in order to survive, and with the mentality in place that "I'm already a criminal, so I can't really fall any further," these people often begin resorting to thievery and other crimes that are not victimless, and are sent to jail. Because the poor have been driven to these crimes, the eyes of the general population are drawn to them, and they say, "The poor are the criminals of our society. The poor cause all of our problems." Their eyes are diverted nicely from the problems of the rich as the enforced problems of the poor seem to carry more weight.
So, in that regard, it does help keep rich people rich. Or at least, it keeps them in power, which, in a roundabout way, keeps them rich.
The person who wrote the article was a professor teaching a class on the American justice system. Ironically, as an exercise, he asked the students to develop a prison system with the express intention of keeping the rich in power (before explaining all of the above to them), and what they developed was almost an exact copy of the American justice system.
