On Sunday, masked gunmen executed 13 people in a drug rehabilitation center in Tijuana, Mexico, just across the border from San Diego. Authorities now think these grisly murders may have been in retaliation for the massive marijuana bust that occurred there last week. Whether the victims were actually involved in the seizure of 134 tons of marijuana destined for the U.S. is unknown, but in the end it makes no difference. It is clear that the tactics of marijuana prohibition are ineffective at producing…