it depends...
if the person exudes a high degree of "know-it-all-ism" without any proof that they aren't really just full of it, I just don't reply. But when people attempt to aid this person in leading them to a more positive discussion, and then start flaming everyone that replies, then they get roasted by me.
Just a thought.
As for me, I just don't post unless I know I'm right, or can argue my point effectively.