And, as always, flagging will be abused to downrank content that people/bots/spammers/scummy-businesses/etc. would prefer you not to see.
This already happens on Hacker News. People frequently flag comments they strongly disagree with, rather than just downvoting them. Despite the fact that the "flag" was originally introduced to flag spam.
Just penalize people for false flagging, and penalize false copyright claims while we're at it.