I agree. I think it would be a lot less drastic of a "ret-con" to make orcs not genetically evil than the ret-cons of Tieflings are an ancient empire of dark bargainers and Dragonborn are remnants of an ancient empire-- both of which just poofed into existance.
They could say that Orcs are a warrior-like, honor obsessed, race of conquerers or barbarians who just happen to often be at odds with humans, dwarves, and elves (like next gen klingons)-- and thus completely valid to have there be half-orcs around-- just as Next Gen has so many half-klingons-- none of which were the result of rapes-- just star-crossed lovers. Next Gen klingons were revealed to have a rich, spiritual culture, with a different value system-- but not inherintly evil (as ToS often made them out to be). They could have done the same with orcs. Heck, I already did that with Orcs over a decade ago in all games I've ever run with them.