Whats the ethical implication of fixing flat feet?

The ethical implication would be malpractice. It is unnecessary for a doctor to operate on flat feet and incapacitate someone permanently. This doctor is using soldiers as guinea pigs and crippling them.

"Say No. You are here to be cured of your wound, not your flat feet. Did you have any trouble with them in the field? No, well, there you are! At present you can still walk, but if once the old boy gets you under the knife you'll be cripples. What he wants is little dogs to experiment with, so the war is a glorious time for him, as it is for all the surgeons. You take a look down below at the staff; there are a dozen fellows hobbling around that he has operated on. A lot of them have been here all the time since 'fourteen and 'fifteen. Not a single one of them can walk better than he could before, almost all of them worse, and most only with plaster legs. Every six months he catches them again and breaks their bones afresh, and every time is going to be the successful one. You take my word, he won't dare to do it if you say No."