I know this is a really common comparison, but I feel like this is also kind of weird. I personally believe both should be legal with obvious constraints in the realm of drunk driving/etc. Basically, do what you want with your body as long as you aren't risking undue harm on others.

Main point though, I don't feel like it's a sound argument to equate the legality of alcohol to the legality of marijuana. Making either illegal is shaky on their own merits and trying to put both in the same category makes both look unfavorable.