This is up for discussion of course, feel free to give your own thoughts and opinions about this
I think Ilias is the good guy in this story, as we see throughout, the monsters always try to take advantage of Luka, even the ones claiming they want coexistence, they all rape him, I think Ilias even points this out at one point. The monsters are selfish and only care about what they want, they don't care about what happens to others and do as they please to whoever they please. The only reason they decide to coexsist is because Luka defeated everyone in high power, forcing them all to submit. Ilias's idea to genocide was a good idea, there was no hope for the monsters.