Macbeth first tells the murderers that Banquo is responsible for their recent misfortune, and then he urges them to get revenge on the man "whose heavy hand hath bowed you to the grave." They assure him that they are men, implying that a man would not let such a wrong go unpunished, Macbeth goads them further by stating:
Ay, in the catalogue ye go for men;
As hounds and greyhounds, mongrels, spaniels, curs,
Sloughs, water-rugs and demi-wolves are clept
All by the name of dogs.
By using this comparison, Macbeth asks them to prove that they are honorable men and not just male in gender. Being honorable means taking revenge: murdering Banquo and his son for the supposed wrongs Banquo has done to them and their family. No true man would let such wrongs go unanswered.
This type of persuasion is similar to that that Lady Macbeth used earlier in the play when she persuades Macbeth to kill Duncan. She plays on the idea of true manhood. According to her, being a man means taking advantage of opportunities for advancement, in this case killing Duncan while he is a guest at the Macbeth castle.
Macbeth assures her that he is surely a true man without killing Duncan:
I dare do all that may become a man;
Who dares do more is none. (Act 1, scene 7)
Lady Macbeth counters with
When you durst do it [kill Duncan], then you were a man;
And to be more than what you were, you would
Be so much more the man. (Act 1, scene 7)
In each case, Macbeth and Lady Macbeth use a stereotype of manhood to persuade. To them, a true man is ruthless, vengeful, and violent.