Public debates are not always circuses. If the debaters are good representatives of their respective positions it is a good way of getting the pros and cons on an issue out on the table. At the same time, there are inherent limitations to the debate format. For example, I find it irritating when an issue that could be the subject of an entire debate by itself is tucked away as one of a bunch of arguments, so both sides deal with it superficially.
At the same time the debate setting is not for everybody. Just as everyone is not cut out to be a blogger, not everyone is cut out to be a debater. Dawkins could have appealed to the inherent limitations of the debate format as a reason for not agreeing to debate.
My problem with Dawkins is that he made this an issue of credentials. Now as an evolutionary biologist Dawkins is at the top of his field. But he has increasingly gotten involved an a crusade for atheism, becoming instead a philosopher of religion. And as a philoospher of religion he is a rank amateur. The most serious concern I have with Dawkins is that the theistic point of view has been very ably defended by philosophers like Plantinga and Swinburne, and William Lane Craig. In addition, there are people in the sciences like Collins and Polkinghorne and Kenneth Miller, who are Christians.
Dawkins has been audacious enough to call a widely held and well defended position, namely theism, a delusion. That's OK if he takes the time and effort to respond to the best theistic defenders in the business. J. L Mackie wrote The Miracle of Theism, (an equally insulting title) but in that book we find detailed critiques of Plantinga and Swinburne. From what I have seen of Dawkins, his book is not a worthy successor to Mackie.