Aristotle proclaimed that rationality is what separates Man from animal.

Machiavelli introduces the concepts of the Ways of Man and Beast.
Man - to use Law and argumentation and reason to resolve conflict
Beast - to use force and violence unto those the Way of Man fails.

Thus, those who are not rational should never be treated as Man. Reason and logic are lost on them, and must be considered to be beasts. So then, they must always be controlled or killed or they will only bring ruin.