In Macbeth Act I, Macbeth kills the traitor McDonwald for his King and country. He guts him from his navel to his neck, as any good thane would. He and Banquo help defeat the Irish and the Norwegians to protect Scotland. These are all "good kills."
In Act II, however, Macbeth commits regicide (killing of a king) and parricide (the killing of a relative) when he kills Duncan. He kills his king, kinsman, and guest: all three are among the worst crimes imaginable for a thane. Killing one's king was equivalent to killing God, according to the Divine Right of Kings.
And it only gets worse: in Act III, Macbeth, as King, kills his best friend Banquo. And he will try to kill Banquo's son Fleance. Banquo's ghost will haunt him as a result.
And it only gets worse: in Act IV, to protect his throne, Macbeth will kill women and children, Macduff's wife and son.
In Act V, Macduff, the hero of the play, kills Macbeth the same way Macbeth killed McDonwald in Act I: he violently kills a traitor for King (Malcolm) and country.