I'm probably gonna get stoned (no pun intended, I swear) for this as I lean conservative...marijauana is a NATURALLY occurring crop/plant, that's what gets me, it's not being "cooked up" in a bathtub with other nasty chemicals, it's a plant that is dried and smoked (ie - like tobacco). I'd rather just smoke a cigar (which I do, probably have a few tonight). I look at it this way, since marijauna is illegal, tobacco should be as well, but what do I know?
In reality, the same should go for alcohol, mind altering substances, right? 
Gambling - it's a-OK as long as the state/government gets their cut - ie, the lottery, etc.
Prostitution - what consenting adults do is their business, not mine. Just tax it and then the government is happy. It's legal in certain counties in Nevada anyway (ie - Bunny Ranch).
This is definitely an interesting thread!