It highlights the complexities involved in implementing a rule against 64-byte transactions (txs) to prevent hash malleation through the coinbase size check. The argument suggests that while such a rule aims to facilitate earlier detection of invalid blocks by simplifying the validation process, it might not be as effective or necessary as presumed. Moreover, the proposal to prohibit all 64-byte txs is criticized for potentially introducing more implementation bugs than it resolves due to the added complexity and unnecessary broadening of checks.

Further, the dialogue elucidates the technical process of validating transactions within a block, pointing out that verifying no transaction in a block is 64 bytes requires parsing each transaction comprehensively. This contradicts the initial goal of simplifying and expediting the validation process by performing an early check based on the coinbase size alone. It is argued that a more rational approach involves utilizing existing validation checks that are simpler, faster, and already integrated into the consensus protocol. Specifically, checking the first input point against null in the coinbase transaction is presented as a more efficient method for resolving the malleation issue than the proposed size restriction.

Additionally, the conversation delves into the implications of the proposed rule on protocol development and consensus changes. It emphasizes the potential for unforeseen complexities and performance degradation resulting from the addition of unnecessary late-stage checks. The critique extends to the broader context of block hash malleation, highlighting that the proposed solutions do not adequately address all forms of malleation, particularly those involving duplicated sets of trailing transactions within a block. This gap underscores the limitations of relying solely on merkle hashing for transaction identity verification and suggests a need for more comprehensive solutions.

In conclusion, the exchange presents a nuanced view of the challenges associated with enhancing blockchain validation processes. It questions the efficacy and necessity of the proposed rule against 64-byte transactions, advocating for a more measured approach that leverages existing validation mechanisms without introducing additional complexity or undermining protocol performance. This perspective underscores the importance of careful consideration and thorough analysis in the development and implementation of changes to blockchain protocols.