An educated society that has legalized access to a product is always the best option, no matter what that product is. In this case, the product is marijuana.
That's the same exact argument used in favor of laissez-faire capitalism, and it doesn't work precisely because the assumption cannot be made that all people are well-informed and can consistently make rational decisions.
It's worth keeping in mind that the FDA exists for a reason. If we legalize heroin, methamphetamine, etc., it would be inconsistent to not open the free market to every drug that's now at all controlled. You think the situation with ADHD and other psych medication is bad
now? Imagine if you could legally buy it all over-the-counter.
At any rate, (hard) drug usage does not only affect the individual. It affects how effectively that individual can contribute to society, and how much he has to take back from it in the form of, for instance, health care. Yes, this includes tobacco, which is legal, but that's a whole other argument there.
You're also missing out on certain economic realities concerning drugs that have performance-enhancing qualities yet are still dangerous. For example, there used to be (I think it's better now) a problem amongst truckers being speed fiends, because it allowed them to stay awake longer, driving longer distances to make more money. The problem here is that if your best performers in a company/industry perform so well because they take drugs (which can have adverse health effects in many cases such as this one, obviously), then the people who don't take drugs cannot compete. In a situation like this, if you were trying to compete in the work force, the economic reality is that you
need to do so or you
can't compete, resulting in either you making money far below that which is standard for the profession, or having trouble getting hired. Same situation with something like professional sports: If steroids are allowed in a sport, you take them if you want to compete well, or else you're left behind, despite the dangers.
You're also discounting the fact that many drugs are horribly, horribly addictive. Nobody can be expected to make rational or well-informed decisions 100% of the time, even those who
can do so regularly. Everyone has weak points, and makes decisions that aren't the best every now and then. However, with the more addictive drugs, all it takes is a short period of screwing up and you essentially become a slave to it. A nicotine or heroin addict certainly chose to partake in those substances at
some point, but it's hardly a choice to continue doing so; they can choose to quit, which is quite difficult and not always successful (and depending on the drug, can be actively dangerous). This is exacerbated by the fact that some highly addictive drugs, such as opioids, can be taken for entirely legitimate reasons for a long enough period to get someone hooked in the first place.
So no, I don't think full legalization of all drugs is a smart idea. Many
health professionals can't even responsibly prescribe certain medications, never mind people being able to shop around for the psych meds of their choice over-the-counter. We also don't live in some sort of Ayn Rand Wonderland where everyone can be trivially educated perfectly and has infinite rationality and willpower. We live in a world where education is flawed, people make mistakes, and not everybody can be assumed to be an expert about everything or even to act rationally, and not even through any fault of their own.
I'm not arguing that the "War on Drugs" has gone well, or been fought properly at all. It's a propaganda machine, which is contrary to the purpose of actually preventing people from doing drugs. I mentioned my high school health class engaging in this; all it does is make people distrust the educators, which is the last thing you want, but which is actually justified in cases like this, because the educators have had a tendency to lie to them. I think we need better, more legitimate education about drugs, as opposed to either the current Official Government Lie Machine
or the full legalization of every mind-and-body-altering substance known to mankind.