Well, the way I see it, alcohol and pot CAN, for some people, be a mere social lubricant. I never got into pot, myself, even in college, and I never partook except in a social setting. I never wanted to get high by myself.
In that kind of setting, I don't think pot is any more harmful to the body or mind than alcohol.
It IS illegal, so I don't condone the use of illegal substances, but I do recognize that some people don't find the illegal aspect of it apalling. Frankly, it's something that I don't care to be around, but others feel differently about it. I think it would probably be best if nobody drank, but I'm not going to insist that everyone else see it my way and refrain from drinking.
The thread, though, is more about when one partner has the right to insist on certain behavior on the part of the other, particularly when the behavior in question is not in that person's presence. I think that's what we are debating, more than whether people should or should not smoke pot.