My gut reaction is to tell you that you're wrong and look for evidence of that, and blame the worst problems of cannabis supply on its current illegality. The illegatity pushes the price up; that high price and illegality attracts criminal gangs who use violence and human exploitation to supply the drug. Making it legal would reduce the cost of the drug and allow suppliers to market themselves as ethical ("free range" / "fair trade" / "organic" etc).
But looking at cigarretes in the UK we see criminal gangs are still involved in the production of dangerous[1] counterfeits and supply of those counterfeits or of smuggled cigarretes from lower tax areas.
But looking at cigarretes in the UK we see criminal gangs are still involved in the production of dangerous[1] counterfeits and supply of those counterfeits or of smuggled cigarretes from lower tax areas.