Your point about Demande also made me think about how the inverse of these situations don't usually happen. As in, we all feel weird today about rewatching Mamoru's scenes because fo the actions of the actor behind them, but we do not feel weird about the actor for Demande who played a character who was on screen doing similar actions.
Maybe I'm misunderstanding your point, and if I am I apologize in advance, but why in the flying [BLEEP] would we feel weird about the actor for Demande playing a character trying to commit sexual assault? Anyone with two brains cells and is over the age of 5 should be able to understand the difference between an actor playing an heinous character and an actor being a heinous person in real life.
Demande is a fictional character. He does not represent Kaneto Shiozawa as a person.
Toru Furaya is an an actual human being who comitted sexual assault and emotional abuse. Mamoru is a fictional character but it's at least somewhat understandable if fans are having trouble separating him from his actor because of the REAL LIFE actions of said actor.