Evil depends on your perspective. If you were an Angel, even a Fallen One, you would have a totally different viewpoint and perspective than mortals, having lived billions of years. Evil is something Mankind invented. The Fallen just dont like Humans and Gods plan because it puts us first. God gave Humans souls and Angels are nothing but soul. I might be a bit peeved too, if after a billion years of worship, he decides to give his love to something else and I would have to think, why should I continue to worship. After all, the War only started because one side of Angels decided to "rebel" , or not to do Gods wish.

From a humans perspective, they want to kill or corrupt us. From a Fallens Perspective they are just poking us with a sharp stick because they can.