You're not understanding his point. He's saying that, in the world where you are Town, killing Arne already serves to make you look bad. It would be a kill made with the intent of setting you up. But in your worldview, Flower is also scum giving you a post restriction, which is a double whammy here that isn't really necessary. The idea behind giving you a Post Restriction would be to make you die from it, and his position is that it makes no sense to do that, and also base the kill off of making you look bad.
I think the point is valid, and should probably prompt a re-evaluation of your worldview a bit from you.