Sometimes though, fights to the death, can result in an enemy fighting harder.You don’t beat fanaticism by a war with rules. You must take the last breath of the last fanatic. Sometimes that’s ugly. Sideliner’s opinions on those engaging the fanatics is not warranted.
You end up with more of your own dead.
And you have a harder time getting intel.
Not saying there's no merit to what you said.
But there are reactions for actions.
One of the advantages to what you said... you don't have to worry about someone later freeing them. Or them escaping. Or people releasing them.