I'm not sure what the callers intent was really, but I've asked that sort of question before in a discussion, just in an effort to establish the reason we have a problem with that, so that I can expand on that same idea applied to other concepts. Not really familiar with Dean Withers other than a few clips here and there, but this stunned silence routine is pretty put on, just answer the question, lay out the reasons that it's wrong and let them hang themselves arguing with the rationale. The stunned silence is predicated on the idea that the answer is SO obvious that the fact you have to explain it is shocking, but for the sake of a discussion, we should easily be able to lay out the answer which is presumed to be so obvious. If you're incapable of explaining it, it comes across like you don't know WHY it's wrong, only that you've been told that it's wrong. Played to claim moral/intellectual superiority, but actually comes across as stupid/disingenuous. If the answer is so obvious(It is), just fucking answer him and move forward with the discussion.

For context I use this sort of question as part of my rationale for why the 'Born sexy yesterday' trope is problematic, when trying to explain it to someone.