St Thomas in this and the next two chapters is not arguing that there is no evil in the world, but that evil has no substantial being, no, nor positive accidental being either: there is no evil substance, there is no positive attribute essentially evil: there is good at the bottom of everything, even of things evil: there is a right use of everything, and a place for all positive being in the scheme of creation. He allows that there may be a substance much out of place, as a bull in a china shop, a bad man in power, an "embossed carbuncle on my flesh." He allows that there are evil attributes, or vices, as the next chapter will explain. But a vice is a good quality overstrained, or perverted. Pride is an inordinate reaching out to high things: but to reach out to high things in itself is a good point in a man. Cowardice is an inordinate care of one's own safety, a thing that one is bound to have some care of.
Of God and His Creatures: 3.7