There's a difference between having seen examples of it, and of it being pervasive and a dominant force. All too often, we attack the weakest arguments of our opponents and ignore the more sane opposition.

There's good reason to ignore the nutjobs and focus on the rational opposition, steel-manning our foe so to speak. It makes our thinking more clear and our arguments stronger.

Even bothering to oppose the insane elements by definition does not convince anyone of anything, since no sane person on either side agrees with the insanity. All it does is momentarily make us feel superior, but it's a fleeting and counterproductive endeavour.