The Prohibition cautionary tale the libertarians like to preach on will not hold with legalizing drugs. Legal booze displaced moonshiners because they had a better product for a good price.
However, Phillip Morris and General Foods are not going to sell crack and heroin and neither are you going to have drugs at state stores in the US the way you have in some countries. Hence drugs will be the field for corner dealers, gangsters fighting for turf and terrorist drug lords EVEN IF LEAGALIZED. The profit margins will be less after legalization, but the massive profits will still be there, providing plenty of incentive for criminals.
I believe that the Nevada proposal called for marijuana to be sold at state stores.