It figures someone from California would come up with this idea!
It boggles my mind that at the same time we (the USA) are slowing the rate of cigarette smoking (nicotine), we are encouraging more and more joint smoking (marijuana). Forget for a moment the drug effects. It is still smoking. A college teacher once told me (and I do not doubt it) that just in terms of lung damage, smoking one joint is the equivalent of smoking seven cigarettes. That fact alone should prove that the idea of "medical marijuana" is a complete fallacy.
It should not be legal (nor should cigarettes for that matter) and it should certainly never be legitimatized by a zoo.
1. Who says it has to be smoked?

2. The "seven times damage"
could be propaganda, let's face it the "drug wars" are not immune from this.
That said, I like the consistency of your argument (banning cigarettes
and marajuana).
Personally I believe the core of the problem is the inconsistency of the authorities, "this (legal) drug is fine, that (illegal) drug is not", which makes them look like hypocrites. Basically, there's drugs and there's water and until people realise that
all drugs have "baggage" a solution will not be found. I'm sure, as in the UK, the US has far more deaths, and problems, from alcohol than all the illegal drugs combined (then again I know you have serious meth problems, something we've been lucky enough to avoid so far). I only read this morning that abuse of benzodiazepines kills more than twice as many as ectasy and cocaine combined in the UK.
The reality is some people will always choose drugs (in the widest sense), some will use them (causing no problems for themselves or others) and some will abuse them (causing problems for themselves and/or society). I don't believe banning drugs will solve this underlying fact/instinct and the best a society can do (like I believe Portugal has) is to help those (who want it) that get into problems. It doesn't eradicate the problem, they'll always be those that chose not to be helped, but it keeps power away from criminals (selling in an illegal market) and avoids criminalising ordinary citizens who just happens to choose a drug that society's deemed illegal.
Personally I don't care what drugs another person chooses to take, it's only when they burgle my house (or cause problems for others in any way) to pay for drugs that I get annoyed -the two are not inevitably linked.
This will be my last (slightly off thread) post on the subject as ultimately it's like a "faith argument" -opinions are usually entrenched and unwaiving so I don't want to waste the energy or posts.