Ppl saying he shouldn't kill should remember that the MC is the villain in this story. Granted, he is looking to switch things around, but he is still essentially the villain, and the whole point of him changing was just so that the actual hero loses plot armor. This is not to mention the fact that the MC is targeted to being killed, so it is better, at least for him, to finish off his opponents. Otherwise, he runs the risk of getting killed himself.