Asgore might not be much of a king but all the evidence is that he was a great warrior, and even Undyne's in awe of his prowess. It's not _entirely_ certain, maybe, but he was the king of the monsters at the time of the Monster-Human War (either that or his dad or granddad or whoever ALSO sucked at naming things, which is possible), in which case he likely killed lots of humans. But Asgore would never be able to pretend that the killing of the seven fallen humans would be morallly equivalent. These would not killing human warriors in self-defence, not hot-blooded slaying. THESE deaths would have to be cold, planned. Murders.