dean wants to be able to tell his lies with out someone there who could dispute each and every one of them. If he goes on separately, he can just spout off a whole list of lies and have no one there to call him on it.
Dean knows that Mehlman will make Dean look like the mental midget that he is. You can only go so far on hate speech - every once in a while you have to verbalize your plan for the country. Oh that's right - there is no plan from the Left except bash the President.
Lets hope Dean goes on 1st at least.