Every weekday at the federal courthouse in Tucson, Arizona, undocumented migrants are gathered in a courtroom and made to face the judge’s pulpit like shackled parishioners. Most of them are young men wearing T-shirts, sneakers, and jeans. Called up in groups of five, they are each asked the same incantatory set of questions: Do you understand the rights you’re giving up? Are you pleading voluntarily and of your own free will? Are you a citizen of the United States? Did you enter southern Arizona from Mexico without coming through a designated port of entry? How do you plead? Culpable,…