If <50% of miners want to censor you, they can make it take longer for your transactions to be processed. If it's >50% (or thereabouts) they can prevent your transactions from every getting confirmed. Sure, the 34% could collude until they happen to produce 6 blocks in a row, but each individual member of that group would make more money by going along with the censorship and not being censored themselves.
I believe it's similar with PoS, but with somewhat different incentive magnitudes.
If 66% of miners censor their own blocks to comply with OFAC, then eventually the transaction will get in.
If 66% of miners not only censor their own blocks, but also collude to continually reorg the chain, then obviously all bets are off, the project has failed, and the exchange rate is headed to 0.
I think the former is infinitely more likely than the latter.
Is it though? If crypto ever becomes a common currency people will still want to transact in it regardless of corruption/collusion among miners. Most are not going to stop using it for ideological reasons like "miners are altering the chain" unless it negatively impacts their own transactions.
This is false. If miners controlling 66% of hash power decide to censor you, they can ignore any blocks produced by the minority who include your transaction.
I believe the point is that there’s no prerequisite that all miners are independent, and will definitely collude. PoW or PoS this is the case, as blockchains cannot prevent IRL agreements.
With PoS, the big players control the small players. If the minority doesn't play along, their funds will be slashed by the procotol. If 66% of validators censor you, your transaction will never be finalized.
With PoW, the big players cannot coerce the small players in any way. Everyone independently controls their own blocks. If 66% of miners censor you, your transaction will merely take 3x as long to be confirmed.