I think that may have been.the approach the Reiners took. It sounds like they were not forcing him into rehab that he didn't want, by the time he was was out of his teens (given the finished movie came out 10 years ago when he was only 22).There is also a growing chorus in the field of addiction medicine suggesting a move away from complete abstinence as the end goal in favor of what’s called “harm reduction.” My own psychiatrist is board certified in addiction medicine and favors this approach. We use it for me for weed & shopping addictions. It’s basically asking “what’s the problem you’re having due to your anddiction? and is there a way to solve it that isn’t stop using all addictive substances forever?”
I also think that stabbing your parents while they sleep is just so far out of the realm of any ordinary human behaviour, that it's probably not the case that he was any kind of ordinary person with an ordinary addiction or ordinary mental health problems, that just somehow went awry by accident or somebody not treating him with the right approach.
JMO
ETA: after all, Lizzie Borden wasn't addicted or showed any sign of mental illness!