It's not wrong, per say, but none of these characters have a leg to stand on if they did, which is why they don't. It makes great sense. Who at this camp fire could say, with absolute moral superiority "The other side is completely bad, and we are justified in killing them"? Nobody because they all have blood on their hands. Gabi, early season 4 could do that (in her propagandized ignorance), but has since matured and even she knows things aren't as simple as "We can only prosper if the island devils survive".