I don't have anything to hand and can't be arsed searching but im sure that some research found that it was newer, stronger breeds of skunk that were particularly linked to psychosis.
In the same way that bootleggers and illicit consumers in 1920s chigaco went for whisky rather than a few pints of bitter, the economics of illegality encourages more potent, concentrated products.
I used to be quite a heavy smoker back in the day. When i started out soapbar/ resin was much more common. I could easily have a smoke then go to the pub a couple of hours later and function normally. It also wasn't too much of a barrier to studying or work.
Skunk is a completely different beast. It can make me extremely paranoid and i find normal functioning much more of a problem.
As a society, we currently don't allow unrestricted sale of unregulated high strength moonshine, because it's dangerous. We tax the shit out of high strength spirits because they're potentially very harmful. We still heavily tax beer and cider, because of health concerns.
It shouldn't be beyond the wit of man to arrange something similar for the range of different products that are unhelpfully grouped as a single thing, cannabis, in the minds of many.