Positive effects aside, legalizing recreational drugs will not eliminate the cartels, but instead will reroute the distribution of their product through "legal" channels. The cartels have sufficient power that the only move left is their integration with established markets. They aren't just going to lie flat while "legitimate" corporations take their spot.

Legalizing has other benefits though, like increasing scrutiny into human- and arms-trafficking, a legitimized drug business will need to shed that part somehow and hide it.