It's all about the money. There will always be a certain number of violent, power-hungry assholes out there, true. Banning drugs and thus enabling a black market in them means that people like that have a way to make money and create organizations dedicated to enforcing their will. Yeah, if we legalize drugs, they'll try to switch to something else to maintain their gangs and lifestyle, but nothing is as profitable as drugs, so there will be much less money available to such organizations, and they'll all either shrink dramatically or fall apart entirely.
It's also about how money influences people. Some people are irredeemably criminal/violent, but I think they're a minority. Most of the people in the market are probably following the money. They're doing it to make money, and they'll use violence if needed to preserve their market, but they probably don't have any desire in general to hurt people. Take away the need for violence by making it legal, and thus delegating violence to the police, and they'd probably be perfectly happy to be relatively normal businessmen.
Then again, maybe they'll just get involved in the Government instead :-/
It's also about how money influences people. Some people are irredeemably criminal/violent, but I think they're a minority. Most of the people in the market are probably following the money. They're doing it to make money, and they'll use violence if needed to preserve their market, but they probably don't have any desire in general to hurt people. Take away the need for violence by making it legal, and thus delegating violence to the police, and they'd probably be perfectly happy to be relatively normal businessmen.
Then again, maybe they'll just get involved in the Government instead :-/