Why is D correct?

The author argues that since hurting others eventually hurts ourselves, those who hurt others must be unaware of the consequences of hurting others. There is a pretty huge flaw here, the author doesn't give us any reason to think they must be unaware. The fact that an action will hurt the actor doesn't prove the actors doesn't know it will hurt them. People act self destructively all the time. Perhaps I know that burning my neighbors shed down will harm me, but I simply detest my neighbor more than I care about myself. To make any sense, the author must agree that the harm to oneself is not intentional.