That's true, but those orcs are not presented to us as moral actors here to restore some preferred order of things on behalf of the opposing faction. They are not vectors for morals. That's the main difference between a character like Sylvanas and a character like Illidan. They're both evil, vile people who are still interesting to the plot, but the game pretends Illidan's actions are somehow justified and moral and that's why he grates on me.
Saurfang is the same. He is an abhorrent person, largely responsible for where we are now, along with having many faults that Sylvanas lacks - indecision, weakness and hypocrisy. But the narrative wants me to band behind him and support him, whereas it burns Sylvanas in effigy. @M-Ra has the right of it. It's the out of whack morality that makes characters like him and this entire narrative detestable.