Don't be an idiot. The people who want to smoke pot already smoke it. There will be no, or at least very little, increase in the people who smoke it, and the laws against driving with it will still be in effect. The fact is Thousands, if not millions, of people drive every day all across America while under the influence of MJ, not to mention Alcohol. Legalizing MJ will actually reduce crime, at least in CA. Take the money out of it and the crime will go away. The only danger is if the government taxes it too much then the illegal growers will still be making money off of it.
It is amazing the amount of people who failed to learn the lesson of prohibition. People drank more during prohibition than they did before or after. Drugs, all types of them, were legal in this country at one time. There were no more addicts per hundred thousand then than there are now and there were no crime gangs killing off people in order to protect their interest in the drug trade.
Want to know why parts of Arizona are off limits to Americans? It isn't because of illegal aliens per se, but due to drug dealers. Illegals are bad enough without having gangs mixed into the picture. Gangs without money are impotent. Drugs give them to the money to arm themselves and to recruit new members. MJ is part of that BS culture. Legalize it and you take part of the money away from them.
Just because one cannot totally stop the occurrence of a particular crime does not mean we should altogether stop trying to control that crime. At a minimum California highway injuries and deaths will increase together with our taxes to pay for the medical care of the victims of drug abuse. Overall drug consumption due to the climate of acceptance.