" if the death of an animal is unnecessary why kill it?...We will never be able to re-wild this planet whilst we are at war with it... "

You've given yourself an example. There are millions of deer all over Scotland that would be required to die before any such "rewilding" could take place.

What point did you actually make about moral philosophy btw? if your notions about the sanctity of life mean: as I've touched on before here, that a deer should be allowed to starve to death or be eaten alive by blowfly larvae rather than be shot and eaten by humans then that's merely placing your own own notional sanctity above both utility and morality.