Why Index Funds Are Like Subprime CDOs

First: When you buy a ETF share for the S&P 500 (iShares, Vanguard etc), the share is not backed by all 500 S&P components. Virtually all the large-number component ETFs are using a sampling of shares to match the underlying index. (They would be buried by transaction fees otherwise.) The subsampling of the index is reasonably well-understood math, but relies on an assumption: That the buying and selling each component share will not be greatly affected by the ETF purchase or sale.

[Edit: I may be out of date - Some ETFs are full samples. Nevertheless, the bigger point that the ETF purchase/sale does not much affect the price stands.]

Second: The ETF uses a very clear process to keep the price of the ETF in equilibrium with the index it represents. Large players are allowed to go to the ETF adminstrator (say iShares) and turn in a bunch of the ETF shares, and iShares will transfer back the underlying components. So if the ETF price ever gets too cheap relative to the index, the big players will redeem the ETF share, and then sell the underlying shares they received, which results in a quick, nearly guaranteed profit.

Conversely, if the ETF price goes above the index, a large player will bring a basket of the underlying component shares to iShares, and iShares will give them corresponding ETF shares. So they buy the components cheap, sell the expensive ETF, again making a quick profit.

Now to what Burry is saying: Several components of the big indices are thinly traded compared to the amount of money in the index funds. In a large index drop, there will be disproportionate downward moves in those thinly traded shares: As large players will be redeeming the ETFs for underlying shares and then sell, these thinly traded stocks will drop further than you'd predict from the index. This will cause the index to drop further, which will cause more ETF shares to be redeemed, perpetuating the cycle.

I think his point should be better known than it currently is: The current wisdom that "you can't lose money in the stock market long-term" is reminiscent of "you can't lose money buying a house."

If you have one trillion dollars invested, and the entire exchange volume is based on me and my friend trading a single share back and forth, everything will still work. It doesn't matter how much you own, because my friend and I are going to want a fair price for that one share in any case. There's no practical limit to how passive things can get before a problem kicks up, as long as a few hedge funds stay in.

Start with something simple, say taxing people of one race 15% more than another race. That would seem a valid form of repression.

Okay, so that rarely happens and is almost always combined with far greater forms of repression. But there are less extreme examples. What about taxing someone more when they have kids, or more when they don't?

Sin taxes also seems a way to repress certain behaviors in society by increasing their cost. Why can't the logic apply in other areas of life where tax rates are unequal?

Passive investing is great. Especially since the S&P 500 has been up for ~10 or years.

It's when passive investing becomes panic investing (sell everything).

Burry's argument is that many of the underlying stocks inside the index have a lot less liquidity than the index funds and securities themselves. E.g. if a lot of capital quickly exits the index funds, then some of the single-name stocks may be overwhelmed by the liquidity. That would result in their prices becoming severely dislocated relative to their true value.

But if you're just buying-and-holding that doesn't matter. If the stocks in your portfolio become temporarily dislocated, who cares? Dislocations by definition correct themselves over time. If some stock falls 50% because of panic selling, without anything having to do with the underlying company, it will eventually return to the correct price. And much sooner than the decades long timeline that you're saving for.

That doesn't mean that Burry's thesis is irrelevant to everyone. In particular if you're an institution that offers liquidity to your clients it may be very relevant. Or if you're a bank, hedge fund, or insurance company that's subject to mark-to-market capital ratios or margin calls.

If stocks become very dislocated, your investors may panic and redeem their money. Or your regulator may say you have insufficient capital and have to liquidate. That's very bad, because you'll be forced to sell at fire-sale prices. However, that's not relevant to individual investors, because nobody can force you to sell out just because your portfolio goes down.