Have you ever been in a discussion where someone is clearly the outlier and it's accepted beyond reasonable doubt that his ideas are extreme?

Another example, imagine you're discussing religion acceptance and a extremist say whoever doesn't follow his religion should die since their are infidels. How do you avoid that completely stupid idea from dominating everything?

Perhaps I shouldn't have given any examples, as it seems I have only drawn the attention of those who care about the examples and not my underlying point.