The main point of Joshua Marquis' New York Times op-ed
seems to be that most people in prison are guilty—that is, contrary to the sorts of things you see on "In Justice" or "CSI," courts don't send an overwhelming number of innocent people to jail, and the handful of death row inmates whose convictions were overturned on DNA evidence represent a very small sample. Overall, Marquis calculates, the court system has an extremely high (99.973) percent accuracy rate: "most industries would like to claim such a record of efficiency."
Okay, even if those numbers are right—and if they are, that's still
no reason to get complacent about the problems with the justice system—I'd add one other statistic here. According to a 2002 Department of Justice study
on recidivism, 51.8 percent of all ex-convicts end up back in prison within three years. Of those, over half go back not for committing new crimes but for technical
violations of parole—a missed appointment, a failed drug test, not landing a job. Most people in prison are guilty? Depends on how you define it.