In some stories Parademons are chosen from the human-ish Hunger Dog population, but mostly (I think) they're shown to be grown artificially. And yeah, they're usually low-intelligence and lacking in individuality, except for various "special" ones. They still have emotions, though. A random Parademon, stranded on Earth in the Cosmic Odyssey miniseries, was capable of thought and feeling (and distress at being abandoned by the collective and Darkseid's will.)

You'd think that everyone on Apokolips should either be mindless or constantly suffering, at least if Darkseid's doing his job right.