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I am going to attempt to explain how Historians reach their conclusions about HJ.
Like my "Jesus-in-a-nutshell" description earlier on one of these threads; I take full responsibilities for all errors and omissions:
Imagine Historians as trying to build a three dimensional Venn Diagram in their heads. They acquire data about Jesus and classify it into different sets, sub-sets and super-sets.
Some of these classifications are; Religious stories, Historical Narratives, Information about the time and place, Anthropological data, Textual analysis, Archaeological data... etc.
This data is then classified according to source and location etc and ranked according to the principles of the Historical Method:
http://en.wikipedia.org/wiki/Historical_method
They don't just make it up as they go along. They have as many rules as any Scientist. Some of it of course comes down to subjective expert opinion, but it's the same for all Ancient History. They have to make the most of the evidence to hand.
They build this sort of holographic Venn diagram in their heads ( writing it all down in their formal Historian jargon, of course) and see where and how this data all intersects.
The reason the HJ varies, is that different Scholars weigh different evidence in their own way. But they all agree on a human being at the intersection of those sets of data.
I hope I'm not misrepresenting it too much.
This is why I go further than Belz... in my opinion. I, after reading all of this data and seeing the arguments, am not satisfied to say "we just can't know".
I'd put my HJ confidence level at about 90% right now. That might change in the light of future information. I can't say.