I feel like the only reasonable response, then, is to start madking all email sent from people who believe this as spam, so they can get a sense of what this feels like.

Seriously, though: people who abuse the system like that,--whether they are giving products bad ratings for reasons unrelated to the product, using the PayPal dispute system as a threat (or seriously on everything they purchase from everyone online as it let's them get stuff for free), or downvoting comments on HN out of retaliation for a lost argument--need some kind of meta-moderation to keep their data from affecting the system.