It looked like an open and shut case. Two dead aughisky, one human covered in blood -- that's not that hard.

Brewster thinks he'd pass on the ability/inclination to kill aughisky. It's like people who don't think you should breed a dog that mauls people. Stormbringer, on the other hand, would think that was a positive trait, and want it passed on -- to aughisky chilren.