well I got plenty of ideas

1 We're trained by a terrorist group that wants to wipe out mankind and replace them with what they call the "homo perfectus" which is us,

2 We're in a Medievalish world where "heathens", which are people who are part animal, are being hunted down.

3 same thing as number 2, except in a falloutish world, where the world has pretty much gone south after a nuclear war, a bunch of people start getting animal traits (fur, turning into a cat, scales,) due to exposure to radiation, Religious groups have sprung up everywhere to slaughter them