You need an objective method to actually determine what is likely to be true and not go by any conviction based on what you think is likely to be right. You cannot be convinced that it is likely that the soul/afterlife exists and neither can you be convinced that there is a likelihood that it does not exist. You would have to remain undecided. Since this is such a simple life lesson to learn, then I have to be missing something here. I cannot possibly be right in saying this because we are talking highly intelligent believers and skeptics with these sort of convictions.
But sure, you can have the opinion that it's undecided. Perfectly fine for you to believe that - it's what I think is the correct conclusion. But others do lean toward certainty or uncertainty depending on the context of the rest of their opinions about reality.