act 3 scene 1

Macbeth convinced the murderers that Banquo was their enemy. In reality, the murderers had nothing to do with Banquo. Macbeth was trying to appease his own guilt by making Banquo out to be a scoundrel. Macbeth claims they are not "men" because they let Banquo ruin their lives. The murderers were only killing Banquo for money. Making Banquo out to be less than men is similar to L. Macbeth's repeated questioning of Macbeth's "manhood". In both cases, they are trying to convince people to do something by shaming their manhood.