Haven't read his book but have read enough of his tweets to understand what he's getting at.

IMU, a belief is a "luxury" one if 

• Adhering to it is considered "harmful" to the individual/society (whether rightly or wrongly; Rob would say rightly, presumably)
• Expressing support for the belief is "trendy," manifesting in particular as the "high-class" people popularizing the belief
• The proponent's "class" allows them to avoid the consequences of the said belief held at scale, whereas the "regular" folk suffer

So, as an example, a "high-class" person comes out with a "hot take" like police abolition, which over time picks up steam and gains more support among the broader populace. When the consequences of higher crime rates hit, the broader populace suffers. But the "high-class" person, by virtue of living a life removed from crime's consequences, avoids them. The high-class (unlike the "regular") person could afford the belief; hence, it's a luxury.

For an own-behavior-relating belief (so, think things like polyamory/drug use, not open borders/police abolition), the steps are similar except the "high class protecting the luxury believer" part takes the form of the "high class" person's safety net, ability to delay gratification, "knowing when to stop," etc. saving them from the negative consequences. Whereas someone poor and divorced from the tacit knowledge behind these behaviors (as elaborated on in more detail by Viliam) is more likely to suffer.

With this in mind, "classmate ... a Republican oil tycoon who extolled the virtues of going to church but didn’t go himself" seems unrelated:

• Attending the church isn't (widely) considered harmful to the society in the US, I'd think, more like meh.
• The tycoon's avoidance of church themselves isn't because they say it's good but secretly know "when to stop" or something. It's just because they're lazy, or something?
• Finally, in terms of long-term effects, going to church is probably not actually going to hurt you? At least not to the degree police abolition etc. might.

There's a lot of interesting stuff in the post, but the following counter-point you offer to "the idea that sleep’s purpose is metabolite clearance" I can't quite follow:

The paper is called “Sleep Drives Metabolite Clearance from the Adult Brain”. The abstract says:

The conservation of sleep across all animal species suggests that sleep serves a vital function. We here report that sleep has a critical function in ensuring metabolic homeostasis. Using real-time assessments of tetramethylammonium diffusion and two-photon imaging in live mice, we show that natural sleep or anesthesia are associated with a 60% increase in the interstitial space, resulting in a striking increase in convective exchange of cerebrospinal fluid with interstitial fluid. In turn, convective fluxes of interstitial fluid increased the rate of β-amyloid clearance during sleep. Thus, the restorative function of sleep may be a consequence of the enhanced removal of potentially neurotoxic waste products that accumulate in the awake central nervous system.

At the same time, the paper found that anesthesia without sleep results in the same clearance (paper: “Aβ clearance did not differ between sleeping and anesthetized mice”), meaning that clearance is not caused by sleep per se, but instead only co-occurrs with it. Authors did not mention this in the abstract and mistitled the paper, thus misleading the readers. As far as I can tell, literally nobody pointed this out previously.

I'm not quite following the meaning that clearance is not caused by sleep per se, but instead only co-occurrs with it bit. So yes, sleep allegedly results in X (clearance), that you can also get through, e.g., anesthesia. I don't see how this is more misleading than a statement like exercise results in autophagy which you can also get by using exercise mimetics hypothetically would be (if/when we had enough data on exercise mimetics, for ex.). Basically, you can get to a good thing (clearance/autophagy) in both of these cases through various means. Why would this be a misleading thing to say about sleep/exercise?

Is the idea that we should be seeking to anesthetize ourselves (without sleep) to get these specific benefits at least, instead of committing to more sleep (which would be an overkill in this presentation)?

Not responding to the broader reaction to this paper in your post btw, just this one bit. Thanks

EDIT: I also want to note that you don't seem to address the role of sleep in immune function/lowering systemic inflammation markers beyond Walker's failures of citations. There's a bunch of literature on this on pubmed etc., which tbf I haven't reviewed in detail so perhaps it's all bunk! But it would've been good to have insight into that, as my impression ATM is that sleep certainly strengthens your immune system and lowers systemic inflammation.

@leggi, thanks, I think the key thing here is that BCG isn't used to protect you against TB here, but broadly boost your immune system. I found a bunch of papers on this (admittedly, many about youth, but also some on the elderly getting BCG):

https://www.ncbi.nlm.nih.gov/pubmed/25725054
https://www.ncbi.nlm.nih.gov/pubmed/21979284
https://www.ncbi.nlm.nih.gov/pubmed/27737834
https://www.sciencedirect.com/science/article/pii/S1931312817305462?via%3Dihub
https://science.sciencemag.org/content/352/6284/aaf1098
https://www.bmj.com/content/355/bmj.i5170
https://www.who.int/immunization/sage/meetings/2014/april/3_NSE_Epidemiology_review_Report_to_SAGE_14_Mar_FINAL.pdf
https://www.bandim.org/-/media/arkiv/projekt-sites/bandim/pdf/bhp-vaccines.pdf?la=en
https://www.clinicaltherapeutics.com/article/S0149-2918(13)00014-3/pdf
https://www.mpg.de/14491738/0219-mpin-116799-modified-tuberculosis-vaccine-as-a-therapy-for-cancer-of-the-bladder

What I want to call out in the context of the elderly:

https://www.ncbi.nlm.nih.gov/pubmed/21979284

The efficacy of Bacillus Calmette-Guerin vaccinations for the prevention of acute upper respiratory tract infection in the elderly.

AIM: to study the efficacy of BCG vaccinations, once a month for 3 consecutive months, in elderly on the prevention of acute upper respiratory tract infection (AURTI), interferon - gamma (IFN-γ) and interleukin (IL)-10 level in the BCG and placebo group and their comparison in the period of the study.

CONCLUSION: BCG vaccinations in elderly, once a month for 3 consecutive months, significantly prevent the AURTI and can increase the IFN-γ level as Th1 response and IL-10 as Treg response in the period of the study.

BCG has also been used for decades to boost immune system in fight against gallbladder cancer, as immunotherapy:

https://www.cancer.org/cancer/bladder-cancer/treating/intravesical-therapy.html

https://my.clevelandclinic.org/health/treatments/17908-bacillus-calmette-guerin-bcg-treatment-for-non-muscle-invasive-bladder-cancer

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4427258/

So given that

a) we know the safety profile of BCG, and people can evaluate if they're at risk of any adverse reactions (largely minimal) from getting it, and

b) it does seem to boost immune system, broadly and against the upper tract respiratory infections in the elderly (in addition to many other studied benefits for youth)

It seems that the negative costs of getting it (refreshed) are nearly 0, whereas the benefits are >0 and potentially great. On this basis, the recommendation makes sense, IMO (for anyone who isn't at a risk of some complication from BCG, based on the safety profile).