Sorry but I don't think that scene is well written. He must be accustomed to the blood and guts of hunting since childhood. He has been killing Bambi's family for years.
Killing an animal is not like killing a person, but an experienced hunter will not suffer ptsd from killing an enemy with a bow. Not only an experienced hunter, he already killed a man with no remorses prior to that. Some of the best snipers in war history were hunters.
Now, after saving the girls and himself from a cult of lunatics, plus saving the world with an arrow, he acts like a bleeding heart retard.
Of course this is just my opinion I find that scene contradictory with his upbringing and previous story.