Yes, but if we are talking about real world problems then we have to deal with people who are dumb and sometimes we also have to convince them to get what we want. It is rational to limit the truth output of a forum of truth-seekers. An analogy would be the intolerance of intolerance. To maximize tolerance you have to be intolerant of intolerance. This is also the case with rationality as you won't be able to make the world a more rational place by telling the irrational folks the truth, namely that they are irrational, that would just result in more irrational behavior.