There is a lot of this "I won't dignify the other side by debating them" stuff going on.

Richard Dawkins won't debate philosophers. Historians won't debate Holocaust-deniers. AGW proponents won't debate AGW Skeptics.

There are a lot of good reasons not to debate - cowardice, time pressure, other commitments, lack of experience, the other side are rude jerks - but the idea that associating with the other side to the extent of sharing a speaking platform - as occurred in this video - is absolutely counter to what a liberal society and commitment to the truth is all about.

Frankly, why would anyone who believes they are unassailably correct not want to use the opportunity for a teachable moment?