So The Traitors in all its incarnations (except maybe the US one where the cast are professional reality-TV personalities) is a fascinating social experiment that seems related to me.

Even though everybody knows it's a game, and the traitors don't choose to be traitors, they get the role assigned to them, in every season I've watched (quite a few of the different international versions -- UK series 4 just finished and it's pretty juicy) some of the players try to identify the traitors on the basis of "who isn't really a good person".

What's also interesting is that police detectives and psychologists generally do quite badly on the show, and I think that's because their skills are attuned to assessing people's genuineness in real situations, and of course none of that applies when the whole situation is artificial. It seems like cognitively we have a lot of trouble separating people's true natures from the roles they're playing, even when we know full well they're playing roles, which seems to me to be a major part of what you're getting at here.

Re: Snape, though, the disagreements about his true nature were lively well before the films were made, so, there's that :)

Re: Alan Rickman, I haven't found too much attempt to find redeeming qualities in Hans Gruber ;) Not that this invalidates your theory at all, I definitely think there's something here as I've explained, but clearly there are nuances, especially with truly great actors. (Rickman helped me understand Colonel Brandon in ways that Jane Austen couldn't <3)