It is easier to control how you relate to a theoretical group than a concrete individual. If you believe it is proper to hate Creationists, you can do so with little difficulty. If you change your mind and think it is better to pity them, you can do that.

But if you landlady has actually helped or hurt you, and you know a strong emotional response isn't actually called for, you're going to have a very hard time not liking or hating her.