At the beginning of the play, you can see that Macbeth and Lady Macbeth are not bad people. Macbeth is seen as a brave man and he led King Duncan's forces to victory. His reward for his loyalty is to become Thane of Candor. When the three witches give Macbeth their first indication of him becoming king, Macbeth starts to think in a different way. Macbeth and Lady Macbeth let their greed take over.
Macbeth had difficulty at first about killing King Duncan, so Lady Macbeth asks the god to take away her compassion and femininity and replace it with remorseless ruthlessness. You can begin to see the descent of her madness. After Macbeth kills King Duncan, he begins to think that killing is his only option. He has Banquo, his best friend, killed to try keep his sons on the throne. He is warned that he can't kill Macduff, so he has Macduff's family killed. Macbeth's greed and Lady Macbeth's ambitions have now begun to lead to their downfall.
We see that Lady Macbeth is descending into madness. She sleepwalks and talks to herself. She keeps saying that she can't wipe the blood off of her. This means she can't get rid of her guilty conscience. When Macbeth hears of his wife's death, he reacts coldly and with indifference.
Malcolm's quote "this dead butcher his friend like queen" shows how far Macbeth and Lady Macbeth let their own greed take over their life. I think the two of them deserve this epitaph, even though there was goodness in both of them. The let darkness take over their lives and it led to madness and murder.