(Liquor running on the Great Lakes was a ma-and-pa operation with very little violence associated until stiff enforcement handed it to Capone's gang.)
I myself am a moderate on the issue: if the social harms of the prohibition of a certain drug outweight the social harms of its increased use under a legalization regime, it should be legalized, if the balance is the other way, it should stay illegal. I just wish people would have the clarity of mind to distinguish which socal harms are cause by drug use and which are caused by giving the trade to criminals.
I tend to say that primary violence (as a means of enforcing contracts) will decrease if drugs were legalized, but secondary violence (addicts breaking into homes, killing the occupants and stealing their goods) will increase. In that case, I would prefer the violence between people who freely choose to take or deal drugs over the violence against people who have no choice in the matter.