Difference is that the taxation of the legalized drugs pays for the programs, so the users are paying for their own resources and not burdening everyone else who doesn't use.  Legalization of pot allowed the new tax revenue to pay for rehab programs that were going to be otherwise cut.  

Legal marijuana has generated a lot of money/jobs/taxes in Colorado.  Instead of burning money trying to fight it (yet people still used), let the drugs pay for themselves.