If QC can hack bitcoin, then it could hack anything including every altcoin, every banking account in existence,
every email, nuclear launch codes, etc. This would trigger worldwide panic and lead to economic collapse.

I doubt the developers of QC including Google, Microsoft, IBM, Intel, etc would allow that to happen.
So I don't think  they would be selling an advanced quantum computer to just anyone. It would be like selling a nuclear bomb
to anyone who wants one. Like nukes QC could very easily be used as a weapon of mass destruction in the wrong hands.

So the QC companies will probably be working with industry and governments to quantum-proof
their systems and networks beforehand. These quantum-proof security measures will likely be open-source
and made widely or publicly available long before advanced QC is ever released as a commercial product.

When that happens then you know the technology has matured enough to be a potential threat, but the security
against it will also be widely available. So to me it's just a lot of needless fearmongering.