In Philadelphia alone, more than 7,000 are arrested each year, mostly for simple possession. It takes about three hours to process each arrest, thereby taking police officers off the street for about 21,000 hours annually. That's like having 400 cops working full time every year just busting pot smokers.
21,000 hours is a lot of time, yes. But 21,000 divided by 400 is 52.5. These "full time" cops are only working fifty-two hours a year! (In fact, it wouldn't surprise me if Goldstein got 400 by dividing 21,000 by 52, although I can't see how that would make sense as weeks have nothing to do with the problem.)
The actual "400" there should be about 10, assuming cops work two thousand hours a year.
I support the legalization of marijuana, but I don't support people that justify it with bad math.