Any drug being illegal is stupid. It's not the government's place to protect people from themselves.
That's why we have laws. If people were smart enough to protect themselves, we wouldn't have to have a legal drinking limit, seatbelt laws, or even laws against polluting the environment. The problem is that not only are people stupid BUT they have a tendency to hurt others when they act stupid.
To me, any drug that is not designed to heal you or help you in any way AND alters your brain chemistry should be illegal. Yes that includes alcohol.
Not only does it bring our general population's intelligence down when they hit the teen years BUT contrary to what you hear, Marijuana does lead to other, harder drugs in the same way that a pack of cigarettes a week can lead to 2 packs a day, and a few beers a week can lead to whiskey daily. Why?
Tolerance. When your body has some form of drug, be it medical or not, in your body often, you get used to it; You build a tolerance. The same effect that was harmless before now doesn't do it for you so you go after more. Few people have the ability to avoid this. Hell, this happens with caffeine too!
I grew up in the weed capital of my little, apple orchard area. I sat next to the weed supplier (he grew it himself) for the whole town during 9th grade math.
He burned down his barn while high.
Next, the girl I had a crush on? Weed. Promised me she'd NEVER do speed. What happens? She started taking speed. Ended up breaking and entering for drug money. Last I heard she was in jail.
And when you're on an LSD trip, you can do some fucked up shit. Unprotected sex, self-inflicted injuries, abuse, rape, and who knows what else.
When you're not yourself, you never know who you'll be.