The problem with the legalization of marijuana is not that it is a "bad" drug per say. In fact, alcohol is just as bad, if not worse (as a depressant).
The problem is the drug "war" that would take place. See, unlike alcohol or tobacco, marijuana has proven itself to be useful as a "real drug". If legalized, i can guarantee that the government would ban the growing of it. Why? So they can tax it of course. It is the logical thing to do if your a big government in need of a few trillion dollars.
Anyways, because it has these medicinal properties, and not just a "drug" per say, the pharmaceutical companies are going to be all over the stuff. Why? Because of the Money, of course! Think, not only could (for example) Pfizer sell marijuana to the sick, and they could sell it to the stoner in your 5th period English Fundamentals of engineering class. Double the profit, right?! But think, how would Pfizer like it if one could grow Viagra (or any other prescription drug) in your house? They would fight and bitch to the government about how they can't "make money off their prescription drug" and how "marijuana usage was getting out of hand" and even "were losing money". I can tell you what would happen, the government would step in. Why? Well they need money too, remember?
And if it was over the counter, same situation. What if you could make Loratadine (Claritin) in your basement; i mean why not, tons of people need it. Honestly, i don't think that would go over well with the drug companies AND the retail chains ( like Walgreens).
So while it may not sound like a bad idea on the surface, and while marijuana may not be the worst thing out there, greed is a bitch. Also, one could argue that legalization worked in other countries right? Well i can pretty much guarantee that those other countries aren't as greedy as America and its drug companies.
(Also, we hear the phrase "alcohol related death" so many times and personally i don't want to add the phrase "Marijuana related death" to the "list").
To that kid in everyone's 5th period English class Fundamentals of engineering: Even if it was legal, you probably wouldn't be able to smoke it legally for the same reason that you cant legally drink: your a minor.