I think the idea is that eventually this won't happen, and there are currencies issued by governments where this happens too, and certainly you wouldn't want that either.
Cryptocurrency will simply have to compete with currency issued by sovereign governments, similar to how government-issued currencies compete with each other now.
I think an issue for many people is that crypto is looked at categorically as a currency, but it could be much more. It could be a crappy currency, but a good store of value (a better version of gold in most respects, though gold retains an intrinsic value), it could also be a great currency - transiting government borders with impunity and anonymity, which may be very valuable to some.
Historically, we've used gold, up until the last 150 years or so (don't quote me on exact timeline here) and even then the U.S. finally went off the gold standard in the 1970s. For most people, cash was still thought of as a store of value - they'd throw it in the bank or under a mattress. Or they thought gold was, but since it's heavy they just trade cash instead that's backed by gold. It'll take a while for the global paradigm shift to occur that pits currencies (sovereign issued and otherwise) against each other as a separate theory to assets in general. Cryptocurrency (which is now a bad name IMO) straddles the borders here, so it tends to be confusing.
Personally I view cash as good for liquidity, but that's mostly it. I want the cash I receive to be turned into productive assets, so I hold a much smaller amount compared to assets.