Tolkien himself had trouble deciding what Orcs should be...
... and one of the issues was the matter of heritability. Was even Melkor powerful enough to make the orkish state heritable?
'(...) though Melkor could utterly corrupt and ruin individuals, it is not possible to contemplate his absolute perversion of a whole people, or group of peoples, and his making that state heritable (...) In that case Elves, as a source, are very unlikely.'
JRRT, Myths Transformed, Morgoth's Ring
But Tolkien appears to have accepted this later in any event, as the corrupted state was seemingly still heritable when Men were considered as the main stock.