Ok, if drugs were legal, the price would probably drop by quite a bit. Suddenly, there wouldn't be nearly as much money to be made selling them illegally, which would in practice probably mean to people who were underage or were too stupid to get the medical marijuana prescription.

Would you shoot someone for 100 grand?  Most traffickers would.  Would they do it for fifty bucks?  Not likely.  More to the point, they wouldn't have the money to bribe cops and politicians like they do now.  

Instead of big time dealers, you would have small time dealers and they wouldn't be able to cause nearly as much damage to society.

This illustrates another problem with having a large part of our borders unprotected.  It isn't just honest laborers coming in.  Some of them are carrying dope.  Some of them are venezuelan special forces types coming in to make sure no airstrikes we might do go unavenged, some of them are probably al quaeda types looking to start something.  Leaving the borders unsecured is STUPID.