Alcohol actually disrupts your brain messages.
Mary Jane depresses the sending of messages.
Alcohol tears up your liver. Sure, it grows back, but should it have to?
Marijuana doesn't destroy any organs, though it can make you wrinkly the same way cigarettes or smoking anything does.
Alcohol has limited medical benefits, such as red wine (one glass only) for stress relief, or as an antiseptic.
Marijuana is used to treat AIDS, glaucoma, some forms of cancer, as a pain reliever, stress reliever, and appetite stimulant. It can increase the lifespan of a terminally ill patient by years without the harmful side effects of synthetic chemicals.
Both are hallucinogens, but I've never known anyone to black out from too much pot, or get marijuana poisoning.
Also keep in mind that anything in excess is a terrible thing, even oxygen.