There is an open possibility that cash will flood into BTC/ETH as a store of value in a highly volatile S&P market, replacing traditional reservoirs (eg: Japanese/other international equities, precious metals, etc).
Erm, S&P's implied volatility is 23.62% / 30-days. Bitcoin's volatility is over 100% / 30-days.
https://www.bitmex.com/app/index/.BVOL
Implied volatility and historical volatility are different, but they're at least "the same units". So please tolerate this apples-to-oranges comparison. Still, its clear that BTC is way more volatile than the S&P500, even today.
In times of crisis, people move their money from high-volatility to low-volatility sources. IE: Stocks to Bonds.
In times of growth, people move from low-volatility to riskier (but higher potential of gains), ie: Bonds to Stocks.
An individual can put cash into an asset. You can start with $1, then exchange it for BTC, and now you have $0. The amount of dollars in your accounts has gone down and the amount of BTC in your accounts has gone up.
But in aggregate, this is impossible. There is a (mostly[1]) fixed supply of dollars in the world. And there is a (mostly) fixed supply of BTC in the world. When you buy BTC for $1, the $1 just moves from your account to someone else's account. Their BTC moves from their account to your account. In aggregate the amount of dollars is the same before the transaction and after. The amount of BTC is the same before the transaction and after.
The reason for this is that for every buyer, there is always a seller. Every single time someone puts dollars "into" an asset, someone else is taking dollars "out of" the asset on the other side of the trade. No one has ever put dollars "into" BTC on net.
Generally, prices do not go up because dollars go "into" the asset. It is fallacious to say that the stock market has gone up because dollars have gone "into" the stock market. Dollars flow through markets, they don't flow into markets. Prices reflect opinions of people making transactions, they don't reflect a history of dollars that have gone "into" an asset.
To be fair, this issue is kind of pedantic and besides the main point of this thread, but I do think it's a fallacy worth being aware of. Ever since I learned of it, my financial thinking has felt clearer.
[1] let's say fixed with respect to you any buy/sell transactions you may or may not execute (this would have be an asterisk, but it turned all of my text into italics)
There are no dollars in BTC, period. Dollars and BTC may both move, and in certain exchanges one may be traded for the other, but the dollars are never in BTC. (Your net worth, which you may choose to measure in dollars, may be tied up in BTC, but no actual dollars are.)
(Perhaps "short" was the wrong word. But it is where people go - with reason - when they're losing confidence in fiat currencies.)