[denethorthefirst]

Yes, the forces of Morgoth during the war of wrath consisted mostly of orcs (and some trolls, dragons, wolves, balrogs) but relatively few humans. No moral problem here, at least from the perspective of Valinor. The moral dilemma of a hypothetical valinorean invasion of a Middle-earth that's ruled by Sauron is that the majority of his armies consists of humans, so the "liberating" elven armies would have to slaughter hundreds of thousands of the people they are supposed to free. That's what Zigur means. But: in my opinion the valinorean army would never have to face that dilemma because most of Saurons human forces would simply mass surrender.