I still don't see what difference it will make if a few large hash power holders "bend their knew". There's still hash power that is not under their control, and as long as the mining farms don't attempt suicide by intentionally reorging, there cannot be censorship.
Censorship is
Any regime or context in which the content of what is publically expressed, exhibited, published, broadcast, or otherwise distributed is regulated or in which the circulation of information is controlled.
source: https://www.oxfordreference.com/display/10.1093/oi/authority.20110803095558166So by definition, censorship already exists as far as
BTC transactions are concerned, the foundation is there and some miners already practice it, so we are past that point already, what you are describing as something that "can't happen" is "banning" transactions, as long as there exist blocks that are mined by any miner that is not participating in the censorship, a complete ban is not possible.
The great danger of all that hash power in the U.S is the fact that they are all subject to the same rules, written by the same group of people, which is why I have always emphasized that the physical centralization of hash power is a lot more dangerous than the centralization of the mining pools, it's worth noting that any hash power that is located in any U.S puppet counties is also subject to same rules.
Bear in mind that I had the same concern when the hash power resided in China, with the expectation that back then another huge portion of the hashrate was located in the U.S. and many other places that are not subject to the CCP's rules, the CCP ban on mining brought great damage to
BTC centralization and we won't see it until it's too late, the U.S government/lawmakers will eventually crack down on a dozen things
BTC related, every U.S miner will have no choice but to abide by the law.
This may be too far stretched but I'd imagine the next big move from them would be the usage of a whitelisting approach rather than black listing, whereby only KYCed addresses are allowed to transact freely on the blockchain, every U.S miner would need to include only the whitelisted transactions, and excuses such "I don't construct my own blocks" isn't going to cut it.
You may still argue that if 25% of the hashrate is out of the U.S reach, all those transactions will still go through once every 4 blocks, but that will also make those transactions a lot more expensive and eventually probably even worth a lot less since they won't be able to "mix" with the other transactions, it would be like having forked
BTC without actually forking it, that's very bad for the fungibility of
BTC.
I think it's quite evident that governments worldwide and especially the U.S did not attempt to destroy
BTC a decade ago when doing so was relatively easy, simply because they understood exactly how it works and they allowed it to grow, and they had a plan of how to control it when the time comes, and as far as things seem to me right now, they have already got the keys -- it's all those large miners located in the U.S.