Controversial views are most likely to stirr up emotional and intellectual reactions. The reactions indicate that something personally important has been touched. Possibly, something that one wasn't even aware of. The real value of the dialogue, however, lies not so much in the ideas being offered but in the emotional and intellectual reactions caused by those views. The views themselves may also be interesting but it is the reaction that counts.
Reactions can also come during moments of silence when tension builds up tremendously.
It can also come from a feeling of disappointment about not getting anywhere and wasting one's time. There is a great potential in this sense of frustation because this is precisely the reaction that we need. Emotions occur on a deeper and personal level. So, by putting the emphasis on the reactions we naturally lead ourselves into the personal dimension. The personal dimension Dialogues are not the only way to get upset.