There are objective measures on which cultures are "better" from an outside perspective. For example, poverty refugees migrating to richer countries. While bringing with them those traits that made the origin countries poor and high in fertility, and gradually replacing the gene pool and culture of the host country. Here is a recent post on these issues. By the way, I believe Hanson is often deliberately general and unspecific when he doesn't want to step outside the Overton window. The linked post has fewer such qualms. Unfortunately being blunt about this issue is upsetting and is often socially punished.
I would advice you and others to be more blunt when advancing your case.
No one – not even you – remembers if we were good or bad, why we fought and why we died...No! All that matters is that two stood against many, that is what's important.
There are objective measures for fitness and quality of individuals, too. But it would be insulting and also kind of weak and evasive to refer to your superior figures of merit in your personal business and contentions. If it is about your personal survival or physical safety, appealing to your goodness, your usefulness, is pretty much the definition of slavishness. (I have never read Nietzsche, just seen some Western movies.)
I'm sure you can see how my point applies to cultures and ethnicities. I understand very well how one gets to the arguments in your comment when dealing with the usual pro-immigration arguments from economists.
Myself, I think it's nice to have a nation of one's own and a homeland for that nation, a country and state owned by that people. Why should we get to have it? Just because.
OP: To me it looks like Hanson is saying the lack of cultural variation and lack of selection pressure on cultures will – to continue with the biological metaphor – lead to accumulation of mutations and loss of function. Whatever your culture values, it will be worse at getting it. Maybe he accidentally introduces his own values to the objective disinterested frame, but it's hard to believe Hanson would make any such mistakes big enough to cause twisting physical reactions of empathetic shame.
Hanson's argument above sounds somewhat plausible to me. What I don't understand is his theory that population bust will lead to stagnation in innovation. Maybe he makes the standard economist assumption of technological progress being a linear function of population (with given level of wealth and tech), which is obviously untrue. Maybe he gives too much weight to innovation in highly specialized fields in comparison to innovations that have more general and generalist applications.
I subscribe to Hanson's substack, and I also do not understand Hanson's repeated exhortations that cultural drift is a severe threat. Indeed, I found the current article from googling to understand Hanson, ha ha. I agree with your summary of Hanson's views. I don't understand the same things that you don't understand.
My own views (of course Hanson would disagree with these): Fertility decline will not proceed to the point that the Amish and Mennonites will dominate in 2 centuries. Why: a lot of things can happen in 50-100 years.
Some possibilities:
Global population may decline and eventually stabilize at a sustainable level. Why: People like having children. Status goals in wealthy countries mean that people are putting off childrearing, but that will eventually smooth itself out. People will start having something like replacement level of children.
At 2024's Manifest, Robin Hanson gave a talk (in his usual sweeping polymathic style) on cultural drift - a phenomenon for which he thinks "there's going to be hell to pay", and about which he is "scared, because this is a really big fundamental problem".
Watch the recording of the 30:00 minute talk here (followed by Q&A).
His argument is roughly the following:
Hanson takes this cultural drift to be a problem. But here I become confused. From what perspective is cultural drift a problem? The obvious candidate is the POV of our culture - if it is not adaptive, it will likely die out. We don't want our culture to die out. But Hanson seems to want to appeal to a perspective outside of our culture:
It seems Hanson wants to say that this is a problem for Humanity, not just for our culture. However, cultures dying out and being replaced by more adaptive ones is exactly what we would expect of a healthy evolutionary system. If our liberal western culture (whatever that means) goes extinct and is replaced by the Amish or Mennonite cultures (as Hanson suggests it might), then this looks like selection working "as intended".
Despite Hanson saying that we should see things "from the outside", all of the specific worries he cites are quite clearly from inside our culture:
I agree these are all bad things. I like technology. I like Liberalism. But if Hanson's whole argument is simply: "if our culture goes away, that's bad!" then why did we need the framework of cultural evolution, the "outside perspective", and so on? Why not just say: "Our fertility is dropping, and illiberal cultures' fertility is rising. If this stays the same, our culture will be overtaken by illiberal ones. That's bad!" ? This way of putting it gets at the exact same worry in a more direct way.
So, maybe I don't understand Hanson's argument. Curious to hear others' thoughts.