Also, by eliminating the dealer you probably avoid many new addicts. Most people need some convincing to get into drugs. If there is no dealer to do that, some people will never start. You still have friends to teach/convince you, but dealers are more than just people that sell a product.
Good point. Dealers are like missionaries, going to schools etc to try to create the next customer base. Dealer: "That guy looks like he had a crappy childhood, a perfect new customer..."