I'm assuming 'must', here, is not some kind of moral imperative (that would be circular reasoning I think), but rather more of an observation: without moral language we'd be a great deal worse at surviving, and one of the reasons we're doing so 'well' is that we have moral language.
So what's the problem there?
In short, Moral Realism holds that moral properties exist mind-independently and Moral Anti-Realism denies this saying they're all just subjective inventions in our head. Empiricists, if they are to hold logically consistent conceptions about the universe, must hold some form of Moral Anti-realism because they lack evidence of mind-independent moral properties (though taking the comments on this story as an indicator they are generally unaware of this).
Hume goes beyond the moral nihilism of Empiricism by saying (1) given that humans insist and are positive moral properties exist and (2) given that Empiricism shows us no evidence of mind-independent moral properties existing and never can due to Is-Ought then (3) the only way that these moral properties actually meaningfully exist is if they were based on a Supreme Being, not subject to dismissal by Empiricism. Otherwise they don't exist at all. From this a lot of people (like Marquis de Sade and his Sadism) took that they didn't exist at all and this is the primary subject human art, culture, and politics has been interacting with since then.
Based on how you use the term 'meaningful', I think you're right in your conclusion. I don't see a problem there myself, because from my (current) perspective nothing is meaningful in any kind of objective sense (I'm pretty much as zen buddhist, or well on my way), but I've had many discussions with non-religious people / atheists who seem inconsistent in this regard. So I get what you're doing here.
Either way, discussing this has piqued my interest in the topic again. Thanks for that.
Additionally helpful was learning, as Edward Leen puts it, that "the chief cause of unhappiness is not suffering". Instead, as Augustine writes, "Happiness is to rejoice in you and for you and because of you. This is happiness and there is no other. Those who think that there is another kind of happiness look for joy elsewhere, but theirs is not true joy." Life often is suffering, but this is not the cause of unhappiness. Unhappiness is caused by not knowing God. As Tozer writes of the supernatural existential "There is a restlessness within us that cannot be satisfied until we rest fully in God."
Humanity really only has two belief systems to choose from: nihilism or the Nazarene, as Carl F. H. Henry puts it. Often, those who most honestly approach the world come to find these two choices and it is not unusual for one to abandon the first for the latter. As former Zen Nihilist and radical convert to Eastern Orthodoxy Seraphim Rose describes it: "Atheism, true 'existential' atheism burning with hatred of a seemingly unjust or unmerciful God, is a spiritual state; it is a real attempt to grapple with the true God Whose ways are so inexplicable even to the most believing of men, and it has more than once been known to end in a blinding vision of Him Whom the real atheist truly seeks. It is Christ Who works in these souls. The Antichrist is not to be found primarily in the great deniers, but in the small affirmers, whose Christ is only on the lips. Nietzsche, in calling himself Antichrist, proved thereby his intense hunger for Christ…"
Either way, I am glad to hear of your interest in the topic and I sincerely wish you well on your continued exploration.
I think this is really where we fundamentally diverge on the whole matter. Perhaps I'm interpreting you incorrectly, but you seem to have found and then left zen buddhism because it's central argument is that suffering is bad in some kind of Objective way. As in: there's an 'ought' in the story there.
What appeals to me is that, as I interpret it, zen buddhism makes no such claims. It primarily argues that suffering sucks, by its very nature, and we seem to be driven to try and avoid it, so we might as well find the most effective ways to do so.
It then offers some kind of metaphysical framework to understand this (with nihilism at its root), but ultimately focuses on practical approaches to deal with this suffering. Some approaches (perhaps most) even make a constant point of not getting hung up on the metaphysics of it all, because that in itself is considered part of the root problem.
I like all this precisely because I arrived at the conclusion that there's very little evidence or use for 'oughts', or any other statements that claim to be Objectively true. And this troubled me for years until I found zen buddhism to provide me with a practical way to deal with this, and some degree of metaphysics and theory (theology, even) to satiate my desire for theory.
So we're both in agreement with Hume, I guess (interestingly, I've found that this is one thing that Christians and nihilist ex-Christians often have in common).
All that said, to make things practical: could you point me in the direction of thinkers or thoughts that might persuade me that there is such a thing as Objective truth, and that there are Oughts?
Eventually though I was stuck by the reasoning in the joke "I used to be a nihilist but then I thought, what's the point?"
If Nihilism/Zen were true, it would not be wrong to think more positively and to deny Nihilism. CS Lewis noted that if one denied nihilism and was wrong the only thing that would have happened would be that one would have paid the universe a compliment it did not deserve. Or as Tim Keller puts it "Aim at heaven, get earth thrown in. Aim at earth, get neither." And I realised my Buddhist/Vedanta aunt and uncle were just driving around in their Prius from satsang to satsang hugging and laughing with Hollywood celebrities and the 1% while my Evangelical friends were reading books to children with cancer at Children's Hospital.
For a direction, Hume is who persuaded me (like the original article notes, he was not an Anti-Realist) and a nice tool for his writings is the versions found at Early Modern Texts. Another useful direction would be the films of Terrence Malick or the polemics of Martin Luther King Jr. Primarily though I recommend the perspective of Erwin McManus (who you can see speak in Los Angeles, on that video at the end of the essay, or from his podcast) who is pursuing things in the footsteps of mystics like Tozer, Murray, Mueller, Francis, and Jesus. For another thinker who is good at explaining things you should listen to Tim Keller's talks available in the Redeemer app at http://www.redeemer.com/r/get_the_redeemer_app -- regardless of what you believe, Keller's frequent and glowingly respectful citations of thinkers like Shakespeare, Derrida, Foucault, Heidegger, Marx and others and his references to all elements of culture, from ancient operas to obscure art films is an amazing breadth that always starts conversations between camps who disagree and leaves any listener, spiritually-inclined or not, with more knowledge than they came in with.
It's interesting that your experience with zen buddhism is exactly the primary 'fear' I have when it comes to the next step of joining a 'community'. So far my indirect experiences have not been positive, and after having wandered outside of (my particular) Christian community for close to a decade I really miss the 'reading books to children with cancer at Children's Hospital' component that was so integral to it all. That's not to say that non-Christians don't engage in this, but just that it feels different. More diffuse and conveniently opt-in. It's one of the reasons I've even considered 'joining the flock' again despite my intellectual issues with the whole thing.
Food for thought, thanks again.
What Hume/Dawkins/I are saying is that human survival/existence is not necessitated by Reason, which is cold and indifferent. As Dawkins says Reason inside the bounds of Empiricism shows us only "no design, no purpose, no evil and no good, nothing but blind, pitiless indifference".