TLDR: Everyone is jumping on the S&P500 bandwagon and bloggers including MMM recommends it, ignoring proper portfolio asset allocation.
The above statement seems inaccurate.
I don't think MMM really recommends it, does he? I recall a blog post and comments where he politely debates this with Jim Collins, pointing as I remember it, to the pretty convincing math of modern portfolio theory... (I'm sorry, I can't find that post right now otherwise I'd provide link. But I came away thinking clearly MMM believes in MPT.)
Large swaths of the Bogleheads community understand and use MPT too. Even if a core, vocal contingent don't. (I dug into this subject a bit here...
Bogleheads Investment Philosophy: Problems with a Popular Approach.)
You know what I think are better and more accurate statements? That investor skill really varies. That most folks are still learning to better understand financial market risk. That relatively few people know a lot about portfolio construction. But happily that lots of folks are learning more and more and becoming smarter, savvier investors...
BTW, if you haven't yet read through the "Rate of Return of Everything" paper, you'll find that illuminating. And it may further influence your own thinking. (Here are my thoughts on the "rate of return of everything" paper:
Lessons from the Rate of Return of Everything Paper and my graphical summary of some of the data sets shown:
Rate of Return of Everything Line Charts. )
And this late postscript: The more I think about the above TLDR reference to bloggers, the more I think about all the bloggers I read who (a) both show real sophistication in their investing but (b) also understand that their readers possess varying degrees of readiness to implement certain strategies and concepts. For example:
Boglehead Siamond recently refreshed the Bogleheads piece on investing around world... Extremely insightful and useful:
https://www.bogleheads.org/blog/2020/03/02/50-years-of-investing-in-the-world-part-1/Tyler of Portfolio Charts does great work...
https://portfoliocharts.com/commentary/ BTW, I'm going to ever go "permanent portfolio"-y... or golden butterfly-y but gosh Tyler's investing ideas are backed up with incredibly sophisticated understanding of investment risk. BTW I say that even though I don't agree with everything he thinks. (Which he would also surely say about me.)
Mike Piper of Oblivious Investor? His soft-spoken, low-key recommendation is a global all-in-one fund--which he's convinced me is a great idea because it's so widely practical and so scale-able. E.g.,
https://obliviousinvestor.com/what-to-do-with-your-portfolio-about-a-likely-pandemic/So the one final thing I'd say is hidden in all of these financially sophisticated bloggers is they don't ram their sophistication down your throat. They all get that most folks are just getting started investing... that most of their audience doesn't have so much money that getting complex makes much difference... that all of us should still be learning.