Re: THC, the active ingredient
"Bathtub gin killed because it was contaminated with things like solvents and methanol"
IIRC the main problem was neither; it was faulty distillation. There's a reason copper stills are used for strengthening alcohol mixtures. Bathtub gin makers were using anything they could get for condensers - often things like steel central heating radiators or industrial pipe - and the steel surface caused unpleasant by-products due to chemical reactions. Also, the distillate temperature range wasn't properly controlled. To get good quality ethanol you need to collect the product over a limited range of temperatures. Methanol boils at about 65C, ethanol at 78C. By not collecting the low boiling fraction, the methanol and acetaldehyde (boils around 20C) content can be greatly reduced. But bootleg distillers simply wanted maximum yield, or were totally ignorant of what they were doing.
Concentrating alcohol by freezing is cheap but leaves in all the acetaldehyde and methanol, so is not a good idea.
One of the best things about marijuana and, I am sure, why so much lobbying was put into making it illegal, is that its preparation is safe and simple.