A tolerance for the propagation of disinformation.
Room for disagreements is necessary, but so is stopping people who never cared about agreeing in the first place. Giving the dishonest this freedom has only silenced the honest by burdening them with layers of crap to cut through before their speech is heard.
A nifty thing, but it's not really addressing the actual problem. The problem with disinformation isn't that it merely exists, rather that it's shoved at such a volume by groups/people who build pseudo-credibility.
Rather than targeting individual instances of disinformation, sources should be dealt with. I think it'd be far easier and more efficient if disseminators were identified and popped a warning.