Because as I read, if there's no replay protection, so for every B2X dumped, there will be a equal number of BTC dumped. If someone sell one B2X, they will be selling one BTC to the same recipient.
You have a misunderstanding of what replay attacks are. It has nothing to do with off-chain buying and selling of BTC or BTX on an exchange. It just means that, under certain conditions, a transaction involving pre-fork coins that is legitimately broadcast on one chain could be maliciously replayed on the other chain.
Because of this misunderstanding, the remainder of the points you are trying to make are invalid.