Marijuana and Alcohol: Different justificatory principles?

What has particularly struck me from today's discussions is how people tend to have different normative views on the Biblical consumption of marijuana and alcohol, and I would be interested in hearing their principled justifications for doing so.

There are two guidelines that I would ask members to abide by:
1. This is a normative discussion. Therefore, the principle that one should, in the absence of a Biblical command to the contrary, submit to the laws of the land is irrelevant. If you disagree or don't understand the point, please start another thread in order to keep this one on topic.
2. Please only comment if you believe that alcohol and marijuana should be treated differently on Biblical grounds. We've all had the abstention-moderation debate before and this is not the place to rehash it -- this thread is only for those who feel that abstention should apply to one substance and moderation to the other. It's the differences in such reasoning that will hopefully prove to be interesting.