I recall -- from years ago -- discussion of this adjective and it's usage in Homer and in Aristophanes. It seems essentially an adjective descriptive of "hard-up" people, working-class people -- "people who live on the other side of the tracks", as viewed from the perspective of the more respectable classes. In Homer it seems to be comparable to κακός when the latter adjective is used in the sense of "worthless for anything that really matters (e.g. fighting, offering counsel in a βουλή). In Aristophanes the adjective is often applied to the clever slaves who are "knaves" who are smarter than their masters and "shifty" or "mischievous." In the course of centuries the adjective came incresngly to have, as did κακός (which originally seems to have meant something like "incompetent," or "good for nothing") a moral sense, "evil" or "wicked." I haven't ever researched the hisory of the word, but something like that seems to account for its gradual change in usage.
Carl W. Conrad
Department of Classics, Washington University (Retired)
ἄτοπον, ἔφη, λέγεις εἰκόνα καὶ δεσμώτας ἀτόπους.
ὁμοίους ἡμῖν, ἦν δʼ ἐγώ. Plato, Rep. 7 (515a)