I'm with
@Doomer: Morally, it is the right thing to do, to keep them alive. If you are living in civilization like ours, that is. With with prisons and country covering law enforcement and stuff. They are not. Their medieval world is like a war zone. What if one of those guy escapes and murders someone 2 week later? Yet again it's not likely in our civilization, but very likely in theirs. We have our ways of doing, because our circumstances allow it (and it is better for our culture in the big picture?) And yet the author inserted moral values into a situation, in which most people would have understood, if she would have finished them all. How will they handle those guys? Those are a lot bandits and they are too few people to securely handle them. You can bet they will try to free themselves. And how will they manage them? Send them to prison? Scold the and let them go? Or will they hang them anyway?
This moral lesson is well meant and could have been done, if it would have been an ambush with 3 bandits on the streets between villages. But when the whole village overwhelmed by (felt) 20+ bandits or something? This feels forced and the MC looks stupid.