Here is a simply laid out article (from CNN.com) highlighting the ever obvious notion that alcohol is far more dangerous than marijuana. The author, Dan Riffle, points out the obvious similarities between alcohol prohibition in the 1930s and the 80+ years of marijuana prohibition that followed, as well as the failures in both. He goes on to point out the many dangers posed by alcohol as stated by the CDC compared to the far less dangers posed by marijuana use.
Read the article and FACTS presented and you can only come to one conclusion. And as someone who has dabbled in both substances from time to time, I would have to agree: Marijuana is safer than alcohol.