Going back to the original question. I would agree that it was probably drugs. Looking at the Dick Cavett interview you can see a totally fucked up person and it only got worse the longer he was in LA
Put that into contrast with the wonderful ( timeless ) albums he made when taking drugs, probably his finest albums ever!
I don't think this kind of pious judging helps, this was personal to him, whereas I believe the only mistakes we can criticize him of are... bad albums, or bad business deals.
Can't have it both ways.