alt Hacker Newsno, it's not a perfect system, but better.
Look at the alcohol market in the U.S.
Or even the tightly controlled Systembolaget [0] in Sweden, compared to the modern markets for cannabis and cocaine.
Tax and regulate lowers violence and increases tax revenue, outright prohibition/making it illegal increases violence and lowers tax revenue.
I do believe "sin prohibition" policies, for not just drugs but gambling, prostitution, etc, are one example of "low-hanging fruit", where there is a noticeably better option that is usually not implemented.
Really, for all trades usually controlled by violent criminals (so everything the Mafia/Yakuza/crime groups traditionally specialize in), I believe that the citizens of a given state will be happier if the trade is controlled by the state and not given over to criminals, which is functionally what "make it illegal" does.