Have you actually heard of anyone overdosing on marijuana? I don't think it works that way...extreme usage might cause vomiting or hypoxia, but those are more a result of inhaling smoke in general...not necessarily correlated to the marijuana itself.
I said that there's the immediate health risk of an overdose isn't there, unlike with alcohol (which you can easily OD on). Technically, you can overdose on hashish or on synthetic THC (like marinol), but there's no risk of overdose with anything approaching normal amounts of smoked marijuana. Maybe there are amounts that you could
technically inhale that would kill you, but that's like saying that you can technically drink enough caffeine to OD. Unless you're actually trying very, very hard to kill yourself, it's not going to happen.
As for hard drugs, I think if we're being honest and objective about it...alcohol is one of the "hardest" drugs around. Apart from hallucinogins, I can't think of a drug that impairs motor skills as badly as alcohol. Alcohol is the only (recreational) drug I'm aware of that can so dramatically affect memory.
Some drugs that are used recreationally can reduce memory worse than alcohol (I know that DXM and PCP can cause memory loss), but in general, you're actually right. I think what most people don't realize is that most commercially available alcohol is very dilute. Beer is around 5% alcohol by volume, and wine or malt liquor is around 10%. You can still get very seriously drunk on it, if you have more than a few beers in an hour, depending on a number of different biological factors. Once you get to liquors, which are usually around 40% to 50% ABV, a 12 oz. can would be very unsafe. Beyond that, overproof rum like Bacardi 151 or neutral grain spirits like Everclear are dangerous without serious dilution. A beer can full of Everclear
would put you in the hospital or the morgue, no questions asked, if you somehow managed to drink it. A 40 oz., like you can get with beer or malt liquor, would probably put you beyond medical help if you somehow choked it through your esophagus.
Alcohol is very definitely a drug. It happens to be our favorite drug in the West (and I'm partial to it myself, particularly in the form of imperial porter and IPA), but I do think that it's disingenuous to pretend that it's not a relatively hard drug in any serious concentration.
If I had to put it on a scale of "hardness" I'd place marijuana above caffeine and nicotine and below everything else.
Nicotine usually falls around the same level as alcohol, because of the addiction and health risks associated with it. I've used nicotine before and didn't get all that much out of it, but you have to be careful with it to avoid addiction, and you can't kid yourself on the point that even low or moderate use has health risks.