If you can break bitcoin, you can also break all the encryption we use for banking and other transactions, so might as well stock up on SPAM and ammo.

It's an on issue, since bank can always switch to face-in-face verification. This is not an argument. Crypto is the problem here.

Beating face verification is quite honestly a far easier thing to break than encryption my friend.

By "face to face" I mean going to bank on your own two legs physically and talking with the teller.

Centralized businesses will not suffer much and will switch. Blockchains will get destroyed due to their immutable nature.

Modern banks don't have the personnel bandwidth to physically verify the identity of more than a few tenths of a percent of their customers on a given a day, at that rate it would take them close to a year to physically verify the identities of every customer once.

For example BofA has ~70 million customers, 3,700 retail branches, if each has three tellers at any given time of operation (generous at BofA these days, where you'll usually find one) and is open 8 hours a day, and average time to serve a customer is 20 minutes:

3,700 * 3 tellers * 8 hours * 3 customers / hr = 266,400 customers / business day

70 million / 266,400 customers = 263 business days

Cryptocoins like Bitcoin only need DSA. Quantum-proof DSAs have been widely known since the 1970s*. Bitcoin only needs to change its DSA - and then everything will be fine.

* see Lamport signatures

Can someone fact check this?

Great question are people predicting we will have enough computing power to "break" bitcoin? How much is needed?

Some portions of bitcoin are immune. Most cryptographic hashes are believed to be quantum resilient, for example.

You just need enough to poison the blockchain

So how to prepare, when?

They can break 1-bit-coin. How's that for ya?