@Duck They are killing the mutated remnants of past civilizations ( see my CS), they are barely sentient and feral. Its not like one big hunting trip, they know the difference between territorial and hostile. These creatures/feral beings seek them out and try to kill them because they see them as invaders. What they are doing would be like removing humans from the top of the food chain, the rest of the ecosystem remains intact while the changes made from removing the prime predator are acceptable.