I'll quote it here. Note that the exact wording may change as we receive further feedback, but the basic message will not.
Why are we doing this?Greater Fool Investing Strategies
Eventually, one runs out of greater fools. - Burton Malkiel
Discussions of investment strategies based on securities or physical assets that have no underlying value or negative expected long term returns are prohibited. Examples include: cryptocurrencies; lottery tickets; tulip bulbs; Ponzi, pyramid, and multi-level marketing schemes; affinity frauds; and market manipulation schemes.
Although the tagline of this site is Investing Advice Inspired by Jack Bogle, we have never previously had any rules regarding the types of investments and investment strategies that could be discussed here. I have always felt that it was unnecessary as I could rely on our members to appropriately respond to questionable advice and ideas. Indeed, in my opinion, these discussions are an essential part of the value of the site.
However in the case of crypto, the message is so dangerous and the backers are so numerous and relentless that we feel we are asking too much of our members who are trying to counter their claims. Also, the sheer number of positive posts about crypto on this site already appears to be leading some unsophisticated investors to believe that these are investments in the traditional sense or that crypto investing somehow has the backing of the Bogleheads community. We have also witnessed what happened to other sites in the recent GameStop saga and wish to have a policy prohibiting any such type of attempted market manipulation on this site before it becomes an issue.
What's our problem with cryptocurrency?
It is my and the Advisory Board's feeling that the cryptocurrency market as currently constituted is extraordinarily risky and should not play a significant role in a prudent investor's portfolio. The risks go far beyond what we are used to dealing with in regulated market securities. like volatility or bankruptcy risk or interest rate risk. Crypto exposes you to non-market risks such as losing the keys necessary to claim your ownership of the tokens, having your tokens stolen by hackers or the operators of the exchange holding them, or having your tokens on an exchange seized by government agencies. All of these have already occurred on multiple occasions. And then there is the largest risk of all. In a very real sense, crypto tokens are already bankrupt. They have a literal value of nothing, they have a future value of nothing. Thus their price depends entirely on whether enough people are willing to ignore this fact and exchange real money for nothing. The only basis for buying them is the hope the the price will go up because it has gone up before. We have a 400 year history of fads like this in the financial markets, none of them ended well,
Note - This policy is limited to discussions of investing strategies. Discussions of cryptocurrencies in other contexts is still acceptable, for example for money transfers or microtransactions or the current thread on crypto trades and tax loss harvesting.
10/19/21 Edit: What about BITO, the new futures ETF?
This still falls under our prohibition. Our ban on crypto discussions is ultimately based on cryptocurrencies' lack of intrinsic value. While the ETF structure greatly reduces non-market risks, purchasing it is still a purely speculative gamble, not an investment.