But the original Amazons don't have to or necessarily even want to eat humans. Hell, that one actively couldn't kill and eat the punk along with the Extermination squad.
I'm sorry you're an edgelord who would instantly open fire on a crowd of relative innocents and someone you were friends with for years.
Mamoru deserves comeuppance for making Lysogenic Amazons, but that's about it. It is totally theoretically possible for the original tiny band of amazons to live peacefully, if they aren't backed into a corner.
As much as I agree with Jin's endgoal as the cleanest solution, the Extermination Squad and Haruka aren't being dumb or evil with their decision.