Folks, I think that everyone is singing from the same hymn sheet. The only difference is in the amount and type of experience of individuals. A novice would not want to kill unnecessarily and may not be sure when to do it, whereas an expert would know exactly when it became necessary.
I would...
Cityman, I empathise with you! I would be in two minds too, especially if there seemed to be a ray of hope. If he doesn't seem to be in pain now I would also be tempted to hang on a little longer. One of our first poults had a toe turned to one side because of an infection that we got treated...