Consternation about alternative possibilities is a result of defining proof and truth as synonymous. If that which can be held as true is that which can be proven then, indeed, one cannot affirm that Luke-Acts was written before Paul died, because I cannot prove it, certainly not if by "proof" we mean "conclusively exclude all alternative possibility." Of course, the opposite is true: if I cannot prove that it was written before Paul died neither can another prove that it was written afterwards. In a discipline such as ancient historiography were I to affirm only what could be proven beyond any doubt then I would have very little to affirm.
Schrei nails the cost of "proofism," arguing that,
[h]istorically, the people who cling to proof as an absolute barometer of truth and only accept the "proven" theorems of the day are inevitably the ones to be proven wrong when science validates the hunches, inspirations, and intuition of its forward thinkers.Spot on. Subscription to "proofism" ultimately retards any scientific discipline, as it cannot advance. Everyone is so busy arguing over the basic issues that no one can move on to bigger issues. This is quite evident in NT studies, wherein we see endless debates over the same, quite basic, things. Yet, as Karl Popper argued, it is not the cautious scholars who advance a scientific discipline, but the wildly incautious ones. This does not refer to the cranks and the loons who argue the demonstrably false, but rather to the person who says "I know that I cannot prove that a is the case but neither can you prove that it is, but I have enough reason to affirm it and thus I will."
It seems to me that the only way to do history is not to focus upon proving every single thing that one says beyond any reasonable doubt but rather to go out on limbs, to affirm that a is likely the case, and thus to ask what the consequences are for b. This is the best way to open ourselves up to new questions. For instance, a question that recently occurred to me, "What about Jesus's operations led to the community of goods?" This is a perfectly valid question that would be virtually excluded under the regime of proofism because there would inevitably be a hundred identical objections: "Well, that assumes that there was a community of goods." Quite so, it does indeed. And, again, so what? It is a perfectly legitimate question: granted the antecedent judgment that Jesus's followers formed a community of goods in Jerusalem shortly after his death what might that tell us about Jesus himself? This is a question that has the potential for significant insight into question, and one that our obsession with proof has virtually foreclosed. And that's really a pity, not just for this question, but for those that would follow from an answer to this question, and for all other questions ruled out by an excessive concern with never saying anything that could be controverted.