The Bible contains stories where professed non-believers, usually for fame, money, etc., beg a showdown with a religious leader. In general, that leadership was unwilling to do so, not because of their lack of faith, but because there was no point in such "debates." Rarely is the non-believer brought to a state of faith; never does the faithful leader lose his faith, and few, if any, watching converts are won from the "error of their ways" (in either direction) from such a meeting.
Indeed, all those who would destroy the faith of the faithful face an uphill battle, rising from obscurity. Who would show up to hear Bob Thomas expound his ideas of why there is no God? How many adherents would he get? Indeed. But who won't show up to listen to the Archbishop of Canterbury defend the faith against heathen secularists? Thus, such a meeting benefits only the upstart radical, while putting the establishment's faithful at risk. To reject the meeting exposes the establishment to some ridicule, it is true, but such name-calling does little to damage the faith of their followers and is quickly dismissed.
Thus, the wise religious leader will quietly pass on "debate." This, I suspect, is the reason why the orthodox Jews, Muslims, and Mormons are unlikely to take Mr. Hitchens up on his offer. The spirit of contention is not from God.
There are, of course, other stories in the scriptures, where those heathens were destroyed, often in a miraculous way--I'm thinking Elijah and the priests of Baal here--and I'm sure that in today's age, no religious leader would like to face the courts as an accomplice to God's wrath, should the miraculous happen again.
