I disagree. Again, in a deterministic universe humans make choices but lack free will, so I don’t think your position here holds water.
Again, I don’t agree here. If they will never make a choice, I don’t think it is accurate to say they can make that choice. If it is indeed possible for them to make that choice, then a lawful good demon should be a valid possibility. If it is not a valid possibility, then it is not true that they can make that choice.
But if their will is free, then there must be the possibility of an instance of one acting contrary. It becomes a valid option for, say, an adventure featuring a lawful good demon ally.
Observational experiments? We’re talking about fictional characters. We must assume that if something is possible within the fiction, a writer can (and probably will) explore that possibility.
Right, and what we know through out of game information is that demons are always chaotic evil, barring exceptional magical intervention.
I strongly disagree. Actors are responsible for their decisions, even if those decisions are arrived at deterministically.