Except regulation would haunted quality. Something illegal trade doesn't have. So you can undercut by cutting which in return makes a product less potent and potentially dangerous. That said, like with pot, most users switched to dispensaries as soon as they were a thing. The ones that didn't just don't care as much about what they are buying and its unlikely to get pot that's dangerous. Tho the ones selling it may be.

It would absolutely make a huge dent in the illegal trade. Maybe boy get rid of it, but help immensely.