HAH! You just uncovered libertarians dirty little secret. They all claim to be for less taxes - smaller government. But in the end - they lie. They support legal dope which leads to the issues you mentioned.
Sorry, but by that logic we should also outlaw alcohol and ammunition...that way they wouldn't be heavily taxed and regulated.
Would I prefer legalization that didn't include heavy taxation & regulation? Sure...but that's not the choice I was given for which to vote. Kind of like Romney in that respect. He wasn't my first choice, but now he's the only (realistic) choice I have.
BTW, you didn't answer my question: Are you in favor of Prohibition? If not, why not?