Once the witches show him his future, he becomes obsessed with speeding up the anticipated coming into power. He is told he will be King of Scotland, so Macbeth makes it happen by killing the King, which casts a shadow of doubt on his two sons, thereby allowing Macbeth to ascend to the throne.
Macbeth is also to blame for the tragedy of the play because without him being so ambitious and narrow sighted the play wouldn’t have turned out as it did. Macbeth was having concerns for killing Duncan and at once point even says “Proceed no further in this business” but his “vaulting ambition” gets the better of him. Macbeth is to blame for what happens after he kills Duncan, without him seeing the ghost of Banquo and shouting it out and also without him overreacting at Duncan’s death there would have been little suspicion of his involvement with the murder, without Macbeth’s ambition and conscience the play wouldn’t have taken the path it did.
Without the three witches intervention Macbeth would he never murdered Duncan. The witches could be considered evil because one of them murders an innocent sailor just because his wife didn’t give the witch a chestnut and the other witches help plot against the sailor by saying “I’ll give the a wind… And I