If weed is legalized then law enforcement will still have to search out the illegal growers and distributors who compete with the government approved industry. The government approved growers and cigarette makers, bakers, etc will have to be inspected for health and quality requirements. Extra taxes will be levied on pot to help pay for education and so on. The cost involved with legalization of pot will only drive the illegal market to higher profits since they could increase their prices to just below the legal stuff.
So let's keep good pot affordable by keeping it illegal!