Unfortunately, this opens the door to censorship by proxy. Like the Hugo Awards "puppies," it enables organized factions to downvote opinions they disagree with, burying them. One red tag per curator per article doesn't prevent this; it only doubles the attack potential: bad actors could downvote both the article and the tag.
So far, downvoting has been contained to effective and honest filtering. I doubt that will be true going forward as the community swells and system manipulators get savvy.
RE: 2 New Curator Tools for Steemit: Green-tagging & Red-tagging