Carlo Gambino wasn't made a Don until 1957, after Vito Genovese arranged for Albert Anastasia's assassination and Frank Costello's "retirement." Vito Genovese called the famously aborted Apalachin meeting of 10/57 to approve Gambino's Donship of Anastasia's family, and to approve drug trafficking, which he strongly advocated. Gambino was in no position to "decree" death to drug dealers in 1957.

As everyone else has posted: the official Mafia doctrine is death for those caught dealing drugs. Otherwise, the bosses look the other way when the money makes its way upstairs.