As I'm quoting someone: " No one will be forcing a joint down your throat", you don't have to take it if you don't want to. As to the whole: It will make it more accessible to children" idea: Uhhh sorry to break it to you, but drugs are MORE then accessible to children, if they're going to take it, they will.
With narcotics legalized, there would be no more shady dealers. Organized crime would be kicked in the balls, hardly. Because without a monopoly the prices would drop. With legal drugs, you would be made to acquire a licence to make/sell, you would be trained how to do it well and safely. It would also be closely watched 24/7 by " Some big brother figure ", to insure this.
Cheaper and Safer. It's simple.