But, let's say what this is really trying to do: push the Legalization activist agenda.
As if that were a bad thing...
In my country (especially its bigger cities) it's almost a weekly occurence that a marijuana-growing operation gets busted. Sometimes big (hundreds of plants), often small (a few dozen plants). Typically this involves a half dozen to a dozen police officers and related personel, driving up to a house and seizing all product, plants, and equipment used to grow the plants. Which likely takes the better part of the day, meaning that's a whole bunch of cops not out on the street looking for real criminals. Product, plants and equipment are usually destroyed, which is capital destruction regardless what you think of marijuna.
If it's a regular house, and happens to be a rented one owned by a housing corporation, the people involved may face eviction from their house. Which has a decent chance of steering them towards a homeless / criminal path with a much, much higher cost to society than that marijuna-growing operation ever had.
Of course that doesn't stop us from criminally proscecuting those growers, which taxes already-overburdened justice system. If 'successful', people may get fines which they have 0 chance of paying since money shortages are a common reason to start a marijuana-growing operation in the first place. In severe cases they may even be locked up, and thus will be non-productive members of society for the duration. Once released, it will be much harder for them to find a regular job, again increasing the chances they embark on a career-criminal path (with asociated costs to society). All these things increases stress between the people involved & their significant others, family, friends and so on. Which helps to increase incidents of domestic violence, homicide, you name it.
Note that all the above is cost to society, mostly paid for using tax money, innocent bystanders footing the bill, etc.
As Europeans, I'm happy to say we tend to be more 'enlightened' in topics like these, and focus more on the practical issues. For example, many marijuana-growing setups tap electricity illegally somewhere. Which is a problem both from safety and economic perspective.
What would legalization do here? Simple: remove the bulk of those costs from the picture. Read: less burdened justice system, more cops out on the street, fewer people evicted from their home, etc. Increase marijuana use? Yeah, probably - a little. It's not hard to get hold of some weed, and those who want to use it will anyway, so legalization wouldn't change much on that front. Why doesn't it happen? Mostly because of an almost religious crusade of people like you, which (imho) are the real obstacle in improving the situation.
Sorry, pot is as much a drug as meth. So is alcohol.
Wrong again. You mention 3 very different substances, with very different properties, and very different problem sets attached. Yes there may be some overlap, but basically: apples and oranges.