Addressing the idea that rhetoric be forbidden because it is capable of evil:
Under such a mode of reasoning, neither will generals, nor magistrates, nor medicine, nor even wisdom itself, be of any utility; […] in the hands of physicians poisons have been found; and among those who abuse the name of philosophy have been occasionally detected of the most horrible crimes. We must reject food, for it has often given rise to ill health; we must never go under roofs, for they sometimes fall upon those who dwell beneath them; a sword must not be forged for a soldier, for a rubber may use the same weapon. Who does not know that fire and water, without which life cannot exist, and (that I may not confine myself to things of earth,) that the sun and moon, the chief of the celestial luminaries, sometimes produce hurtful effects? […] And so, although the weapons of eloquence are powerful for good or ill, it is unfair to count as evil something which it is possible to use for good. (Institutes of Oratory II.xvi.9- 10)
And to think, he wrote that almost 2000 years before Heidegger or the Nazis.