I think you mean argument from ignorance. That would apply if I were arguing that Muhammad didn’t exist, or didn’t write the Qu’ran or that some traditionally recounted facts of his life were conclusively erroneous. I’m not. What I’m pointing to are the lack of evidence to confirm the traditional story that Islamists tell. And I am pointing to how that parallels the historical situation of the founders of other religions such as Buddhism and Christianity. Basing one’s belief on the factual validity of pre-modern history is a shaky proposition because history is almost always a matter of probability not certainty. Existence makes absolute demands. Religion is existential. A firm basis for belief must be based on the first person spiritual experience. The value of traditional teachings is in their efficacy in evoking and supporting that experience and it’s ethical expression in the world.