[arnavs]

You're right to distinguish between currencies with exogenous demand (like USD) and those like BTC. But the "bank run" comment makes no sense, even for beanie babies.

Bank runs exist in a fractional reserve context -- because banks lend out their deposits (which stimulates growth), your listed balance is actually an IOU. That is, an obligation to "cover" deposit balances, which can be met or not.

Now think of people trading beanie babies. One person sells a beanie baby, the other person parts with $10k. What is there to "cover"? Who is keeping what in reserve? The answer is nothing and nobody --- in a world where beanie babies were currency, this would be perfectly fine.

tl;dr you actually need (fractional-reserve) banks for a "run on the bank"