I don't know if they are that comparable. I think that so many people were drinking alcohol that it was just not a good idea to keep it illegal. I can see some future parallel arguments between the two, but let's face it, through about 40 years of commercials marijuana is the demon and it's going to take a lot more delicate work to decriminalize it. It's comparable to if a compelling study came out tomorrow that cigarettes are actually good for you. People would be taken away from their comfort blanket and naturally be defensive initially. Only through education of it's benefits, will people become comfortable and finally accept marijuana.
P.S. - I don't drink and I CERTAINLY don't agree with the fact that alcohol is legalized and marijuana isn't. It hasn't ever made sense to me. I certainly don't like being looked down upon when I say that I smoke marijuana because of an anti-marijuana campaign launched forever ago based on outdated studies and statistics.