What, what, what? The theoretical legalization of marijuana is hinging on its harmful effects? Apparently I have entered a Twilight Zone in which alcohol and tobacco do not exist

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Seriously, I for one won't debate the harmful effects of marijuana. Short term memory loss, helpless stupidity, and, in some cases, debilitating apathy about elements important to your life, like hygeine, employment, and a social life.
But you could apply all of those symptoms to alcohol, respectfully, except for alcohol (and tobacco's) addictiveness.
Also, it's important to keep in mind that if I promote legalization, that doesn't mean I don't have a problem with kids sparking up a fatty. That's kind of silly. Regulate it and tax it. Severe fines for those caught growing it without a license. I don't think personal pot gardens will be such a problem, not compared to bathtub gin, or pouring rubbing alcohol through a loaf of rye bread.
Just treat it like alcohol. Can't drive and smoke. Can't drive while high. Can't smoke in a public place that doesn't have a license. I prefer pot over alcohol, because pot doesn't make you sick, doesn't make you think you can take on 300-pound Kung Fu masters, and is an order of magnitude less likely to negatively affect your life.
But it won't happen any time soon, with the pharmeceutical industry. Also, don't overlook hemp legalization, which the logging industry would put up an impressive fight against.
Alcohol is a drug. Cigarettes are a drug. Chew is a drug. Only one of them has some mildly positive health effects. Marijuana, however, has been proven to provide many health benefits.
A college friend of mine turned to marijuana when no legal antidepressant could help. Even though it's supposed to be a depressant, marijuana lifted his gloom and allowed him to be a successful, energetic, and social individual.
Marijuana is also a decidedly non-violent drug. You will never jones for marijuana. If you think you're jonesing for it, you've never tried heroin. That, my friend, is jonesing. Friend of mine had this anecdote, where he was asking someone how they'd quit marijuana, and the guy said, "I haven't quit. I just haven't scored in eleven years and two months." Marijuana will never do that to you.
Pot proponents will never be pushy.
"C'mon, man, have a drink! Loosen up! Drink it!!!"
"Never had a cigarette? Take a puff, be a man."
Marijuana?
"Hey, dude, you want a puff? No? Okay." Share and share alike. No one gets down on you if you don't want to try it. It's not for everybody. It's not a rite of passage. Just a thing you might want to do to have some fun, to lift your spirit, to take care of a headache, a stomach ache, etc.
Okay, no more rambling from me. If you don't like pot--that's your thing, I respect it. If you know somebody who became a loser because of it--yes, that happens. Though usually that's a symptom of a deeper problem in their life, not the pot itself. Unlike alcohol and tobacco, which can manifest their addictions irrespective of your life experience.
I personally think everyone should try it once. It's not like it makes your head explode or anything

. Don't want any? That's cool.