I'm not a fan of Sam Harris' account of morality either, and I've argued against its scientism. I have a different view of morality's objectivity, basing it on pantheistic aesthetics. But that's a separate matter because the issue here isn't whether morality is "objective." The issue is whether morality in general can exist, given philosophical naturalism. Holdsworth strawmans naturalism, and I show that once we credit emergent levels of nature, we can make sense of the basic idea of morality, which is that things should have been otherwise. Once we can imagine counterfactual scenarios, and make value judgments (thanks to the emergence of minds), we can contrast how things are with how they should be. Problems remain, as you say, about whether morality is more than just opinion. But that problem affects theism, too, via the Euthyphro dilemma.