I liked the ending, at least my interpretation of it, which appeared to be different from most everyone else's. To me Layla wasn't evil in the body of the story, and she didn't turn evil at the end. She's not planning to be a brigand. She's planning to be a vigilante. She has devoted her life to God by training in the Lodge. That portion of her life is now over, with her forceful ejection, and she is now disillusioned with the Lodge as a manifestation of God's will on Earth that it had previously appeared to be. She has lost faith in the Lodge to be what it claims to be, but she has not lost faith in God. According to the Lodge, she's now a heretic, but just because you're called a heretic doesn't mean you should give up your faith and make them correct. To me, her faith is truly unshakeable, and she has chosen to fight on for God's causes in whatever way she can, no matter that she will damn herself further in the eyes of the world. She believes God has given her a skill at swordplay and so she is going to use that sword to fight for God's justice. And, really, isn't that an ultimate test of faith, whether or not you will continue on in your course no matter what anyone else thinks?
FWIW, I'm choosing to ignore the line about finding lots of red scarves, because that didn't make any sense to me, whether she was a brigand or vigilante. Another red scarf would not have the same significance. Bundles of red scarves even less so.
As for the story as a whole, I found the first half or so extremely slow, where they all had the same argument over and over again about the red scarf, and everyone kept saying the same arguments over and over again. When it actually got to the judgment is where it got interesting for me. Yes, the characters were perhaps black and white, but I don't really see that as a problem. This is the story as told by Layla, and she sees it as black and white, hence justifying her choice to become a vigilante.
And I am curious how the judgment of souls would go when there was no treachery. It was only resolved here through poison, but in ordinary circumstances, what is expected to happen? Do the two men just sit there until one of them passes out from dehydration?