Not sure what Vitalik is talking about but it's not about TX replay. If you move ETC it will also move ETH on the other chain, and vice versa. This will probably mess up tons of dapps too. Seeing that ETH still has more value per token than ETC it's certainly in ETH's best interest to protect that value and prevent TX replay. Not to mention that they are the ones on the fork and failed to execute said fork in a responsible way.

And as a general advice, please stop listening to Vitalik, he's way too emotionally entangled in this. Find some real facts, look at the code, whatever. Don't take somebody's word at face value (from either side of the debate).