I'm going to play devil's advocate. I agree that there is a lot of indication that we do, in fact, have pharmaceutical and alcohol epidemics already. But we are stuck with pharmaceuticals and alcohol.
- You can further regulate pharmaceuticals, but you ultimately need them for medicine, so they are going to be around.
- Alcohol is linked to a ton of crime, but its such an ingrained part of our culture, that it would be extremely difficult and probably counter-productive to try to make it illegal.
So accepting for argument's sake that "Pot is less harmful than either"--which is probably true from a certain angle, but is often argued too forcefully without really weighing the whole story--why should we legalize it?
We have proven that we can't deal with the drugs we have, and that they cause a lot of BIG issues.
The libertarian argument seems hollow. I agree that generally people should be able to make decisions for themselves and live with the consequences in their own lives. But the fact is the consequences flow very directly to spouses, children, and communities. Drug abuse is not victimless at all.
The strongest argument to me is that it would eliminate organized crime on some level, which may be true, but that is a VERY different argument than arguing that it is harmless. Its basically deciding which harms are more desirable.
So as for me, I think we need a more careful approach that doesn't just take the libertarian, or hedonist, or big-business "pot is fine" argument at face value-- and create a new problem on top of the others we are already struggling with.