From my understanding of Steems rules, this isn't how it's supposed to work.

Steem, the blockchain, has no "rules" around when or why to upvote or downvote content. It is very simply a stake-weighted crowdsourcing system for rewarding content.

The reason you and many other people are confused or have misunderstandings about that is likely from the fact that steemit.com uses the term flag instead of downvote and has added their own list of "acceptable" reasons for doing so.