I do think this is probably what happened.
I deal with drug addicts a lot in my line of work. I don't have a problem with helping them, but in a way where you don't expose yourself. Actually trying to help a family member with a drug addict daughter right now. Doesn't help when you constantly bail the drug addict out of trouble. But this guy really seems like a sick sociopath.
I am really sorry I ruffled so many feathers. Seems some on this board are very sensitive about this, which is kind of mind-boggling to me. I just don't want this mistake to happen again. I'm sure it won't.
Like you I do a lot of work with drug addiction and have it inside my family. I will point out what I think you know - that when you know someone is an addict/has been an addict, you really scrutinize their actions to see if they have evidence of a return to drug use. Actions, eyes, demeanor, etc. You are quick to notice those things and make corrective actions/sever ties/whatever is appropriate. As long as you don't see that you try to make them feel included and ready to go forward. Help them. You may not be looking incredibly closely at broader personality types of issues.
This situation though doesn't sound like a drug issue but a more fundamental issue with character/personality that he couldn't put up with some new rules that were introduced as GT/CJP tried to make the line between him and GT more clearly defined. He then went off the deep end but it wasn't to the best of what we know drug induced. Now you can make a case that an addictive personality has issues but I know multiple addicts that as long as they are not on alcohol/drugs are salt of the earth and don't need to be worried about. If they come with bloodshot eyes or slurred speech I will shut the door on them. Possibly forever.
In this case I don't see how the blanket "never deal with an addict" statement can stand up to scrutiny. If you want to switch it to CJP should have known his general personality was incredibly vindictive then OK - knock yourself out. But it doesn't seem that this was an issue of addiction relapse that wasn't detected or caused the issue.