What can be proven? What does that term even mean? It's used in mathematics all the time. But, as so many threads I've seen take care to point out, just because evolution is a "theory" doesn't mean we doubt that it might be correct. Science just doesn't use "proved."Sure it is. It can't be proven so there is doubt, what is unreasonable is insulting and attacking those who are acknowledging that fact.
I can doubt anything. Including my percepual faculties. The question is how reasonable is it to do so? History, like the other social sciences (if one puts it in that category) and science in general revolves around weighing evidence to test hypothesis. Probabilistic approaches are common as ways of determining whether or not to accept a hypothesis. For example, a great deal of scientific researcher either uses a known or estimated probability distribution and researchers determine whether their results are so unlikely (often the alpha level is is .01) that the probability their results were random chance are very, very, very small.
With history, we do the same thing. If Jesus existed or didn't exist, we have to look at the evidence and test either hypothesis against it to determine if it has any validity.
Every single mythicist argument I've read, from those written by people who have some expertise in something (there are very few), to the far more common popular versions which are based on fundamentally misunderstanding just about all of the issues, fails to adequately explain how we can look at the evidence we have and accept the mythicist hypothesis.