A reader writes:
Gillespie is wrong -- legalization of weed generally leads to higher prices, not lower (have you *seen* the prices in Amsterdam?). Of course the sin taxes are a factor, but it also shouldn't have been hard for a free market fetishist like Gillespie to see the other reasons.
Once it moves off the black market people have a lot more choices of product and aren't limited to whatever their connection has this week, and so many start choosing quality product over the only stuff that's available, which provides upward price pressure. You also open up the market to consumers who often feel there's too much risk vs. reward in participating in the black market, which also drives up prices as demand increases and a more affluent clientele enters the market (many of us with straight, non-pro-athlete, non-writer jobs can't afford to have a pot bust on our record...).