As a moral question, there are two angles that springs to mind (I am sure there are more, but I don't feel like writing an essay).
1. The liberty to do whatever you want to your body as you see fit, or indeed, whatever you want so long as it caused no harm to others. It's my default stance on life, but it's on the assumption that adults -are- responsible enough to be trusted, and I have many times been proven wrong.
2. The moral question aspect of consuming those in the first place. And I am including alcohol and cigarettes to the mix. Those are legal, tolerated, and in some cases, encouraged. Yet personally, I think that alcohol is a great invention, just not for consumption, and the world may not have been a worse place if cigarettes were never invented (we'll never know). But they are here and given their high acceptance, they are here to stay, and asking whether they should be banned too is kinda pointless. You are about as likely to ban those widely accepted substances as you are to ban religion.
For me, 1 and 2 present a conflicting dilemma. Legalise it, and I think we'll be opening a valve that given time, we won't be able to shut if we wanted to (I think that there is as much chance of legalising all drugs as there is of banning cigarettes - I certainly would not want to spend my life campaigning for either). Is enlarging the market size of substances people regularly consume, and unfortunately sometime abuse a morally positive decision? *Shrug*
By the way, I didn't vote. This topic interest me about enough to make this one post, but I am honestly quite apathetic to it. If it was legal, I wouldn't be calling for it to be made illegal (unless we are actually better off than now than we would be if it would be legal - but I think that's anyone's guess). It's illegal, I wouldn't sign a petition for it to be legal. I probably mentioned in the other thread that I have marginally more interest in being able to legally firing bullets into a decommissioned vehicle in a controlled environment, but that's not to say that I care enough about to make to campaign about it. Life offers more recreational activities than I have time or money to indulge in, even after the removal those I can't.
Yes, I've pretty much repackaged what I said in the other thread. Then again, everyone's already gave their opinion, and I bet it's going to be about the same between the other thread and this one.