So an episode of The Return of Chor Lau Heung (1986) starring Michael Miu and Simon Yam was on, and it was the episode where Zhong Yuan Yi Dian Hong tries to assassinate the Bat Prince but fails and is heavily wounded. He winds up getting rescued by a Buddhist monk, and a conversation about vengeance ensues.
Yi Dian Hong says he does not want to kill anymore, but he is being forced into looking for justice and vengeance, so must kill again. The Buddhist monk counters with his mentality being similar to the philosophy of the Seven Injuries Fist, where he must hurt his own body before he is able to hurt the enemy. He goes on to say that he is not Buddha, the Buddha is not Buddha, but the world is Buddha; all entities are part of a single entity and that by seeking vengeance and killing another entity, he is merely killing a part of himself.
Yi Dian Hong then says that even the Buddha himself slayed demons and destroyed evil beings in order to preserve justice and good in the world, and what he is doing is the exact same thing. The monk them replies with Amitoufa over and over again with the conversation ending.
My question is on how accurate the philosophy given by the monk is on Buddhism, and what is wrong with the way Yi Dian Hong is thinking? The Buddha did slay demons and destroy evil (according to my knowledge and folklore), but why are they not considered part of the single entity that makes up the universe, and who judges what is considered part of this world and what is not? I am not really trying to look for an argument for or against the thought, I'm mainly wondering if the ideas given are accurate to Buddhism.