For discussion, what's wrong with the statement "if you hold a money market cash position [you hold] the same thing as Bitcoin [or a crypto ETF]"? Or, say, you hold one of Vanguard's Gold ETFs. (Good faith)
You don’t own the exact same thing as bitcoin. A money market cash position is backed by money market instruments whereas bitcoin is bitcoin. A gold etf is backed by gold holdings. That’s not the same as bitcoin either. It’s like saying a baguette is the exact same thing as a mac and cheese. It just isn’t the same. You might like them all equally, like some but not the others or like none of them. Any of those positions is fine because it’s your money - but it makes absolutely no sense to think they’re the same.
Money we are using now is backed by obligation of people to pay it back and very well developed institutions that enforce it.
If you hold 100$ you know someone, somewhere needs it to pay their debt. If you hold Bitcoin no one ever needs to buy it from you unless they hope they can find a bigger sucker later.
Instruments in money market are of the kind of: "give me 100$ now and I will give you 101$ 3months later". Bitcoin is not backed by such contract. It's only backed by the hope of finding a bigger sucker later.
I don't think Vanguard offers a gold ETF. (Gold ETFs do exist, Vanguard just doesn't do it.)
I'm pretty sure there's a lot of evidence that gold is a great inflation hedge but otherwise doesn't offer much in the way of returns on a long run basis. Which is a reason in various cases to hold or diversify into it over a money market fund (essentially over cash). That said, currently crypto has not proven itself to be either much like cash or much like gold.