I do not think the benefit of Hanlon's law is intended to be predictive. It seems rather more like a commentary on how our beliefs about people tend to be self-fulfilling prophecies.

I just think it is a clumsy version of giving someone the benefit of the doubt. Is a social grace you can grant people to not look too closely at what they are doing and assume the best about them. And in moderation it is a good thing to be doing. It is definitely not a good approach to analysis of academia or government however, which is where I often see it used, usually to defend ones outlook or respective 'team'.

edit - it also makes me very suspicious about Hanlon. Maybe not the first person I would trust if they tried to play dumb.

I think it is mostly useful as a self-check for the types of people prone to paranoia. I easily develop that sort of mindset and it's been a huge help to my personal worldview.

That is a good use for it. Perhaps the Murphy's Law series is actually a collection of koans from an occult western zen tradition.