I don't think they're being unfairly scapegoated. Oxycontin was an epidemic in itself. I've seen plenty of evidence from a variety of sources that their pills were aggressively and deceptively marketed as non-addictive, and that their wide availability led to an increase in opioid abuse. That includes knowing people who started on opioid addictions with brand name oxycontin and having heard countless anecdotes of the same. I'm having trouble understanding the motive for minimizing Purdue's role. The deception in marketing and all its consequences belong to them. It's difficult to imagine they merely made a mistake in trying to be effective marketers as opposed to knowingly misrepresenting what they sold in a way that was likely to harm the public.

All that said, I generally favor your stance that ending prohibition would yield the greatest harm reduction.