Among the arguments for legalizing marijuana is that the black market for pot will disappear, thereby ending a destructive battle in the war on drugs and conserving valuable police resources. In Oregon, however, pot’s oversupply has delivered the opposite: a thriving underground market forcing legal growers to compete with cartels and illegal grow-ops, with everyone scrambling to move product in a saturated market. In City Journal, Steven Malanga examines some of the unintended consequences of Oregon’s liberalized pot laws. Should Canadian authorities expect the same?