I completely disagree.

Completely?

I think that should the question arise, an action should be explicable to some degree.

Okay. In part I agree with you. I said in the post: “If it is required, just ask the player to justify it out of the game, perhaps to the other players. “Yea, I decided not to do it because my character had a change of heart… he just deep down wasn’t evil enough”. That should be enough.”

But I’ll throw this at you. Would it be acceptable if a player’s answer was “I didn’t want to play that…” or “I didn’t want my character to be the cause of it”? Because if a player is honest, this is the answer you may get if you want them to be explicit. And this answer has to be acceptable.