Macbeth essay question?

The witches don't tell Macbeth to kill Duncan; he decides to do that on his own, and furthermore clearly recognizes several good reasons not to do it. When Banquo gets prophecies of his own descendants' future greatness, they don't cause him to do anything evil. Clearly the witches and their prophecies don't necessarily cause people to do bad things; people decide on their own what their actions will be. It's his knowledge that he has done the wrong thing that leads to him trying to protect his ill-gotten power by being a tyrant, not anything the witches do or say.