I have often seen a thread get posted where OP is completely out-of-line, incorrect, misleading, etc. and then the users that reply, call them out, provide proper information, etc. are given an extensive amount of merit. Under the suggestion you propose, it would appear as if OP was receiving the merits for their topic, when in reality those merits are effectively "anti-OP". I don't know if I explained that properly, at all, but the couple of merits within this thread have gone to The Pharmacist, for explaining why your idea doesn't fit, and it wouldn't make sense to attribute those merits to your thread/post.