Normally, a person has to commit a sin for a good reason in order for it to be forgiven. Macbeth had no reason other than his own pride, wrath, lust, envy and greed. He should not be forgiven.
Macbeth commits most of the Seven Deadly Sins and breaks the Ten Commandments. First of all, he commits murder several times. He does this with callous disregard for justice or the value of human life. Macbeth is a fallen hero who should not be forgiven for his sins.
From this perspective, Macbeth should not be forgiven for his sins. Although Catholics will forgive even these sins, they are terrible sins that destroy one’s character and chances of getting into heaven. He commits the less forgivable Deadly Sins.
Macbeth’s first sins are envy and greed. He desires to have what Duncan has. He consorts with witches and then kills Duncan.
Stars, hide your fires;
Let not light see my black and deep desires:
The eye wink at the hand; yet let that be
Which the eye fears, when it is done, to see. (Act 1, Scene 4)
Macbeth also might be acting partly out of lust, since his wife is the one who eggs him on. She essentially tells him he is not being a man if he does not kill Duncan.
When Macbeth realizes that Malcolm and Macduff have run away, he commits the sin of wrath. He is so angry at Macduff that he has his family slaughtered. It is Macbeth’s pride that makes him feel that he should be king, and his pride and wrath that is his downfall.
Of course, the Ten Commandments also say that man should not kill another man. He covets, steals, and bears false witness in covering up his crimes by accusing others.
Here lay Duncan,
His silver skin laced with his golden blood,
And his gash'd stabs look'd like a breach in nature(125)
For ruin's wasteful entrance: there, the murderers,
Steep'd in the colors of their trade, their daggers
Unmannerly breech'd with gore. (Act 2, Scene 3)
Macbeth does not see his actions as wrong, but he seems to feel a modicom of guilt when his wife dies. He realizes that life is short and pointless, and from that point on prepares to die. His pride is again his downfall as he is convinced that he cannnot be hurt.
A person who is king should be a good leader. Macbeth is not a good leader. He takes the throne from a good king, and does nothing to help his people. He lets his kingdom go to waste while he throws banquets and raises an army to defend his new title. Since he did not kill for any good reason, he does not deserve to be forgiven.
If you want a counterargument, the only way Macbeth might be forgiven is if one considers that he acted under possession from the witches. However, even if he was under their control, they could not have gotten him to do those things if he did not want them deep down inside.