Two must-read op-eds from last week explain why ending marijuana prohibition is perhaps the only effective way to curtail the ever-increasing violence plaguing Mexico: In The Washington Post, Hector Aguilar Camín, publisher of the Mexican magazine Nexos, and Jorge G. Castañeda, a former Mexican foreign minister who teaches at New York University, write that California’s Proposition 19, which would legalize marijuana for adults, “may, at long last, offer Mexico the promise of an exit from our costly…