We always get these 3 options.
1. MC gets recruited/summoned by humans, they call demons/beastmen evil, they actually are.
2. MC gets recruited/summoned by humans, they call demons/beastmen evil, they're not and the bamboozled hero switches sides.
3. MC gets recruited/summoned by demons/beastmen, they call humans evil, they actually are.
When are we ever going to get the fourth option, where MC is tricked by the underdog demons/beastmen into helping them, but turns out the humans were right in killing them?