You can generate valid alternative Ethereum PoS histories in private without getting slashed: just don’t propose them to network? This is unlike PoW, where even

You can generate valid alternative Ethereum PoS histories in private without getting slashed: just don’t propose them to network? This is unlike PoW, where even generating the history is expensive. This leaves a problem: how should new nodes joining the network know if the version of history they’ve been presented with is ‘honest’. The answer for Ethereum PoS is ‘checkpoints‘, but it’s not an ‘objective‘ measure, unlike ‘chain with most work’ in PoW. Even Vitalik admits this, it is why he invented the term ‘weak subjectivity’, he is totally explicit that this is a fundamental weakness of PoS: the valid chain is subjective. The only question that remains is whether the economic incentives that have been designed are good enough to work around this weakness and guarantee whatever properties Ethereum network users have decided is important.