Beginning a debate is all about catching the audience and judge’s attention and coming quickly to the point. Think of it as a trial. You are arguing against Macbeth. You need to drive the point home immediately. Focus on the things that make Macbeth terrible. He consorts with witches. He killed his best friend. He killed the king for no reason. He framed the king’s sons. He had Macduff’s wife and son killed. He is causing the kingdom to dissolve into wretched chaos. Does that sound like the kind of leader you want?
Beginning with a list of crimes Macbeth has committed will get the audience’s and judge’s attention, but there is nothing more valuable than turning the culprit’s own words against him. Point out that even Macbeth himself does not think what he is doing is right.
He's here in double trust:
First, as I am his kinsman and his subject,
Strong both against the deed; then, as his host,
Who should against his murderer shut the door…(Act 1, Scene 7)
Does that sound like a man who thinks he is committing a just act? No! Even Macbeth is aware that his actions are wrong. That’s why he hallucinates about being accused of murdering sleep and sees Banquo’s ghost at dinner. He knows he is wrong. From this point, you can launch into your speech.