I've seen terrible cannabis growers (polluting etc) that are in the black market (the free market). I've also seen them in the legalized (monopolized) government market. And I've seen excellent growerrs in the black market, and even a few excellent growers within the legalized cannabis market.
I think other drugs (like ecstasy) do tend to lead to a lot worse production methods. Something about cannabis being a natural plant, not a lab chemical. And maybe in the way cannabis makes us feel... peaceful and more at one with the planet than some other drugs.