The PIE source is positive, because it was applied as a euphemism in Latin to what would have been laevus (cf. Greek λαιός), from the PIE word for "left." The Greeks, too, preferred euphemism to the direct term for "left": the much more common term ἀριστερά ("left") is a constrastive/comparative derived from ἄριστος, "best," so it means the "bester side."
