In Macbeth, why does Macbeth choose evil over good when the witches tell him his prophecies?
Macbeth initially decides (in Act I, scene iii) to take the higher road after hearing that he will be king.
If chance will have me king, why, chance(155)
may crown me
Without my stir.
He quickly changes his mind after being pressured by Lady Macbeth in Act I, scene vii.
It were done quickly. If the assassination
Could trammel up the consequence, and catch,
With his surcease, success.
Macbeth knows that he will be able to take the throne if, and only if, Duncan is dead. Therefore, Macbeth chooses to end Duncan's life in order to possess the throne. The idea of being king is far more important to Macbeth than being good.
Later, Macbeth decides that he must know more about his future. In order to ease his mind, Macbeth decides to revisit the witches and find out more about his future. Unfortunately for Macbeth, he fails to see any other meaning behind the prophecies outside of what benefits him. He misreads each of the prophecies, told to him by the "masters" of the witches. Macbeth dismisses each of the warnings the spirits give to him.
Essentially, Macbeth chooses evil over good again with his failure to recognize that any good could come from interpreting the prophecies as foreshadowing his own demise. He believes himself too powerful to submit to the fact that he can be overthrown. His overly ambitious nature forces him to, once again, to evil.