St Thomas here speaks, as philosophers always speak, in the universal, not of this individual and that. No natural kind or class, as such, either is evil or is the subject of evil qualities, i.e., of privations of what is due to nature. The kind, as such, has all things that it is proper for its members to have, though sundry members of the kind are wanting in some of these things. There are one-eyed men, but mankind has two eyes: there are invalids, but the race is healthy.

Of God and His Creatures: 3.7