The issue of assumptions is something which Christians and skeptics should resolve up front before beginning any discussion or debate on the truth claims of Christianity, in particular, the Resurrection. If skeptics assume that the supernatural is impossible, then of course, a resurrection is impossible. If Christians assume the existence of their miracle-producing deity, Yahweh, then of course a resurrection is the most plausible explanation for the evidence related to the rise of the Christian religion.
I suggest that in order for a productive conversation to take place between Christians and skeptics, the skeptic must accept the possible existence of the supernatural and debate the evidence with this possibility in mind. In return, the Christian must do one of two things: Prove the existence and supernatural powers of Yahweh (not just of a generic Creator) prior to beginning the discussion, or, prove that supernatural explanations for alleged events such as the Resurrection are more plausible than other possible naturalistic explanations without presuming the existence of a miracle-producing deity.
Unless the two parties are willing to come to this agreement, these debates will never provide a satisfactory resolution. Both sides will walk away from the discussion declaring victory, but the opponent will never believe he has been defeated.