Come on, you are not that silly or naïve. You must realise perfectly well that this situation is exactly analogous to the case of a witness testimony given before the jury in a court trial.
We are in exactly the same position as a Jury - we are judging the witness testimony of the biblical writing to decide if what it says about Jesus is or is not evidence to show that Jesus was a living 1st century human.
I'm curious. Are you saying that this is how historians approach history now, except for (say) questions around the historicity of Jesus? Or are you saying that this is how historians should approach history, but they aren't doing it that way now? If the former, can you give me an example of how historians approach the historicity of some other ancient figure, on whether he or she existed?
Oh, I’m perfectly happy to acknowledge that many people do regard this sort of thing as credible evidence of Jesus. Clearly bible scholars like Bart Ehramn and “almost every trained scholar on the planet”, do regard such words in Paul’s letters not merely as “evidence”, but actually as absolute proof of a human Jesus.
You do seem fixated on Ehrman's claim of certainty. Why keep bringing this up here? Have others on this board expressed that degree of certainty? Why should I care what Ehrman thinks on the level of certainty?
Most people on this board range from "probable Jesus existed" to "highly probable", which is my own view. I think that the sources we have make it very difficult to determine what that Jesus did and said, so we can not recover much about the HJ, to the point that he might as well have not existed. But I don't see the evidence suggesting anything other than that there was a historical person called Jesus who was crucified under Pontius Pilate, then apostles claimed they had visions of the risen Jesus, and this resulted in the birth of Christianity.
If you would like to quote the actual passages and ref’s that you are thinking of, then we can discuss what those passages actually say and where Paul actually got such ideas.
OK. Below are some passages. Tell me where he got those ideas.
Paul calls Jesus a "man" (anthropos) and that Jesus came at some point after Moses:
Rom 5:12 Wherefore, as by one man [anthropos] sin entered into the world, and death by sin; and so death passed upon all men [anthropos], for that all have sinned:
13 (For until the law sin was in the world, but sin is not imputed when there is no law.
14 Nevertheless death reigned from Adam to Moses, even over those who had not sinned according to the likeness of the transgression of Adam, who is a type of Him who was to come.
15 But not as the offence, so also [is] the free gift. For if through the offence of one many be dead, much more the grace of God, and the gift by grace, [which is] by one man [anthropos], Jesus Christ, hath abounded unto many.
Can you point out where Paul got his idea from in the OT that Jesus was a man who came at some point after Moses?
Also:
1 Cor 15:20 But now is Christ risen from the dead, [and] become the firstfruits of them that slept.
21 For since by man [came] death, by man [anthropos] [came] also the resurrection of the dead.
22 For as in Adam all die, even so in Christ shall all be made alive.
23 But every man in his own order: Christ the firstfruits; afterward they that are Christ's at his coming
Note the "now" and "the firstfruits of them that slept" above, suggesting a recent event. Where did Paul get that information?
Finally, please don't conflate Paul's use of "gospel" with "everything Paul knows about Jesus", unless you want to explain WHY "gospel" should mean that.
Just out of interest - have you read any books from those authors; Ellegard, Doherty, Helms, Wells?
I swapped hundreds of posts with Earl Doherty on the old (now defunct) FRDB board. IMHO Doherty's theories are pretty out there. Even Carrier says J:NGNM is 90% speculation. Most who read his books don't have much idea about ancient beliefs, so they tend to swallow his theories without much skepticism.
You can read my review of "Jesus: Neither God Nor Man" from the link just below. He has a number of pages on his website addressing my review and my other criticisms. Links to his responses can be found in my reviews:
http://members.optusnet.com.au/gakuseidon/reviews.html
I've read bits by Wells, lots by Acharya S, nothing by Ellegard and Helms. I'm not really interested in the historicity of Jesus. As I wrote above, I don't think much can be recovered with any reliability. But I DO care -- a lot! -- about what ancient people believed about their world and their gods; it is a topic that fascinates me, and I don't like it when mythicists (or anyone else for that matter) misrepresent those beliefs, which is why I have concentrated in the past on Doherty and Acharya S, who are the worst offenders in that regard.
Or does all your belief in Jesus come from reading authors sympathetic to belief in Jesus?

Wow. Let's try that expression out. "Authors sympathetic to belief in Caesar". "Authors sympathetic to belief in Abraham Lincoln". Nope. Doesn't scan. Sounds like a Freudian slip there.
As explained previously, my belief in the historicity of Jesus as a Jew who was crucified under Pontius Pilate comes from the credible evidence that is available to us involving Paul's letters and the Gospels. If Paul's letters were shown to be forged, or the Gospels were shown to be written as fiction, I would need to re-evaluate my conclusion. At the moment, it seems sound.