The US federal government requires every business to accept US currency in all denominations. Thats why when people drop a pile of pennies on the counter, the clerk doesn't tell them to go to hell. That, in and of itself creates legitimacy of green paper rectangles with numbers on them.

The concerning thing about bitcoin, and any cryptocurrency is that by nature, the larger it gets (as in total outstanding coins), the more difficult it is to create more currency through reconciliation. With traditional currencies, it's relatively easy to print money. Printing money is done mainly to keep an agreed upon healthy inflation rate of around 2%. Why this is important is when deflation happens, loans are no longer attractive because it's always better to wait because items increase in value relative to the currency. In other words, why would I borrow $1000 today when that same loan amount would buy $2000 worth of stuff next week. When people stop borrowing, it has nasty economic implications. (Money Multiplier effect and all that).

That's probably a horrible explanation by me, but the short version is crypto, since it's harder to create over time leads to a natural deflation that increases over time.

FWIW: I don't know a whole lot about crypto, but the things mentioned are concerning to me. I mean it might be a good time to follow the herd so to speak, as long as you know there will probably come a time when the herd runs off a cliff.