every existing blockchain network, including the Bitcoin network, can freeze the funds in an account, as long as all the block producers on that network agree to do so
I thought it was hilarious when he said blockchains shouldn't be able to freeze accounts. Like... really? Could you explain how the super-majority on Steem can stop the other 3 witnesses from including those transactions? There is like some kind of veto round and their block doesn't get included if they try to process it?
Just like witnesses can choose not to include transactions in their blocks, they can also choose not to include blocks in their blockchain.
In such a case, witnesses that agree the block shouldn't be included will build the same local chain on their systems. Witnesses that don't agree will build a different chain on their computers that includes it.
At some point, there's code that tells the witness to switch to the longest of the two competing chains (although even that can be changed via software).