Macbeth is his own worst enemy. He's Thane of Cawdor; he's got a devoted wife; and his king thinks he's the man. He should be happy and content, right? Instead, he overreaches—and ends up dead.
Unless, that is, you think that Macbeth isn't responsible for his actions, after all. Maybe the real antagonist is fate, and Macbeth is just a poor fool who ran into the wrong witches at the wrong time.