There is not Always a Good Guy
I think that just because most of the time our stories have people who are 100% good and 100% evil that often we think that it can’t be a good story if it doesn’t have this. However, I think that the best stories (Harry Potter, To Kill a Mockingbird) have people where they don’t quite fit into this mold perfectly. Harry Potter in book 5 is a jerk that nobody likes, and Scout doesn’t get along with her aunt. Yet these stories still have lessons to teach and also even if they don’t they’re still good simply because they’re down-to-earth.
I think that while the monster says that he didn’t come to teach Conor a lesson of kindness he’s still giving a lesson and I think that he outright tells conor what that lesson is. People are not always perfect and perfectly evil.