It is a little bit like that! Although, I would argue (from what I know of the United States Constitution) that that sort of high level documentation should be more a guide for the specific laws that are actually needed to govern. Sort of like saying, you shouldn't lie, but sometimes it is necessary, just not all the time! That and the fact that the document (whilst being well meaning) was written in a completely different age, and shouldn't be read too literally, especially as we know that the evolution of language renders a modern interpretation of the literal words risky.
To be honest, I can't speak of cannabis, I'm afraid I just don't know enough research about it to comment with any certainty! However, I do know about alcohol, and whilst enjoying the occasional drink, I would have to say that it's negative impact on society is probably far worse than the softer recreational drugs.