what fear does banquo express?

Banquo fears that Macbeth might want to take the crown by illegal actions, such as murder. He fears that the witches have inspired Macbeth to want to be king too much and that Macbeth will do something illegal and immoral. Banquo continues to fear about Macbeth until Macbeth finally has Banquo killed. Banquo simply does not trust Macbeth.