The link that matthew provided is pretty funny. Goes into talking about "crack babies" and LSD Flashbacks... people getting raped, etc.
"Tell that to a woman who is raped by her boyfriend while he was high on PCP. Or tell that to the six year old that is raped by that same guy...."
Aaaaaaanyway... you'll find that most arguments against legalization of it are either incredibly extreme, flat out uninformed, or based on some random generalization (ie "Drugs cause violent behavior".. while at the same time these exact same people also claim video games and movies cause violence [extreme]). You could just as easily rape someone or murder someone when drunk, or sober.
You damage your body just as much (if not less) than someone addicted to cigarettes.
This is one thing where I've actually sat and thought about for a while, "Is there any leigitimate reason for marijuana to be illegal?"
I haven't found one, nor have I found a single person who can provide one that simultaneously doesn't sound like a hypocrite (for example, "No see, alcohol is different because..").. that is, unless the person also thought tobacco, alcohol, caffeine, aspirin, etc.. should be illegal as well.