I agree, it isn't good to lie, but I don't think I will need to lie. When I do talk to the kids about marijuana, as I intend to, I will tell them my true feelings about it - that it is an herb that helps people's pain, and that for a variety of bad reasons, it is illegal in this country, etc.
But keeping my own use a secret until they are old enough to understand seems the best way for me - it isn't as if I would deny anything- if I was ever asked, I would sit them down and explain (just like when they ask me about sex!) but until that point, they needn't know every medicine I use, anymore than they need to know what daddy and I do under the covers....
I feel the same as you same as you about alcohol; if there is a choice, I would much prefer kids smoke pot at home and munch out and watch a movie or whatever, than to drink and drive around drunk- And if pot wasn't illegal, I would have no problem with the kids smoking once they were 18.

It's just that our kids are going to be adopted orphans from a war-torn country, whose limited command of the English language and post-tramatic stress and various other physical and emotional concerns are going to be more important to me initially. It isn't the average family scenario, that's for sure.

Since I stopped drinking in 1984, I have been an inveterate truth-teller, but I will postpone broaching the subject with the kids until they are ready to deal with it. That is what seems the most sensible right now...