Today, for a change of pace, I've decided I'm going to try to think of a list of things that I think can be questioned on moral grounds, or on the grounds of their social cost, but should be legal - since making them illegal causes more problems - but carefully regulated, and that are worth taxing to recover the full social cost of the enterprise.
Sharp pointy things
This list is sorted by approximate increase in mortality caused by allowing them in the US, so far as I could tell. Prostitution is at the bottom, because as best as I could tell from the comparative statistics and studies, legalizing prostitution seems to actually reduce prostitution-related mortality. Curiously, it's the least lethal two at the bottom that are most often illegal in this country.