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.
Worried about brigades too... but it's a pretty general worry, we know there's nothing really stopping the same brigades from using the existing downvote (or upvote) for their nefarious SteemIt-gaming purposes.
What encourages me is that down the line (with millions of subscribers) although the brigades might be able to censor dissenting minority opinions off of "trending" or effectively "the main page", even then, users who are specifically interested in certain tags should still see these particular subjects they want rising to the top of their private main page list, if green-tagging and red-tagging are in place, doing their job.