Of course one can deny the truth of Christianity without having a good theory as to how the movement started. One can appeal to the improbability of the resurrection story itself, and using broadly Humean reasons, maintain that even though you don't know what did happen, it couldn't have been a resurrection. Even if you were a theist, you could dodge the conclusion that Jesus was resurrected. That wasn't my point.
My point was that skeptics seem to lack a story about the founding of Christianity that makes sense. I said that if they had one, it would make Christianity seem less You had swoon theories, theft theories, hallucination theories, going to the wrong tomb, etc. In fact, skeptics in the 19th Century actually attacked one another's naturalistic theories of the origin of Christianity. Skeptics about the founding of Christianity still have pretty widespread disagreements as to how it all happened. One plausible story from the skeptical side has yet to emerge. That, to me, is an interesting fact that supports, but of course does not strictly prove that Christianity is true.
Anyone who believes a world-view has to live with some difficulties. This is a difficulty for every world-view except Christianity.