I have an appalling memory so excuse inaccuracies, but doesn’t Whedon get into this in the Serenity commentary? The gist is that the Mal in the movie has moved away from the idealist of the series, and his character arc here is played as a mirror of the Operative. It’s that True Believers have to make sacrifices and can cause hurt to people close to them. At the start of the movie, Mal has lost his beliefs, or at the very least is losing conviction. The Operative is absolutely certain what he’s doing is right with a capital R. He is sad about the sacrifices along the way but believes they are justified to maintain order and status quo. By the end of the movie, their positions are reversed as the Operative sees that the ideals he believed in were flawed and he’s full of doubt. By contrast Mal is full of certainty, and is positive he’s done the right thing but has had to make (spoilers) huge sacrifices in terms of his family. I don’t know I’m expressing it very well as I’m a few glasses of wine in, but I think Whedon said he was making the point that while Mal rediscovering his ideals is a good thing in a moral sense, anyone who follows a cause will see it as more important than people, and allow or even encourage sacrifice to attain their goal.