If you just think of it rationally, you'll realise any industry benefits from free labour. Organised crime is involved with cannabis because it makes money. And they use slavery illegally to increase their profits (like corporations squeeze as much as they can out of their employees). It has nothing to do with the nature of cannabis or its users. All the weed I've smoked in the last two months was grown by people I know in fields and houses. I think it would be pretty hard to only smoke weed that is tainted with slavery.