They would build a quantum computer intentionally for Bitcoins case to frack the 'Shalecoins'. ('Shalecoins', coins with no owner '
https://bitcointalk.org/index.php?topic=5134441.0)
Banks can freeze accounts, rewind, correct it.
But Bitcoin can't.
Only applies for Bitcoin address where it's public key is known
I'm mainly thinking about the arson scenario. If adversaries were able to destroy faith in Bitcoin this way, I'm not sure how much confidence would be left in any cryptocurrencies.
Few cryptocurrency claims to use quantum-resistant cryptography, so few of those could use the momentum to be cryptocurrency with highest market cap or replace BTC.