That's just silly. Marijuana isn't a replacement or alternative for tobacco. Most people I know who smoke, smoke both. Banning cigarettes would mean the lost of many jobs and a ton of tax revenue. It's never going to happen.
Also, since you mentioned it, it a shame the go to argument that everyone seems to have for MJ is that "it's safer than cigarettes." Cigarettes: A product that every year causes a number of deaths comparable to the entire 4 years of the Holocaust. "It's safer than cigarettes" can be said about anything. A Jewish person living under Hitler's bed in 1941 was safer than cigarettes.
Full disclosure, I smoke neither. Tried both (and alcohol) when I was a teen and didn't like either.