Personally, I'm in some doubt whether a historical person named Jesus even existed. The thing to realise, however, is that it doesn't matter, which is just as well because it is, in fact, impossible to conclusively prove any historical person existed based only on official histories. Archaeological evidence backs up a lot of historical figures, and it is far less of a problem problem for anyone who was recorded on film, tape, etc. once they were invented, but if you don't have any of that, you can't ever be certain based only on second hand accounts.
The reason it doesn't matter is obvious when you think about it. Whether the person actually existed or is just a fabrication, the only thing that actually affects us today is the assertions and actions attributed to them.
Let us assume, for example, that there was no evidence whatsoever, other than textual accounts, for the existence of Napoleon Bonaparte. How does he affect us today? Well, he is recorded as having influenced military thought long after his demise, but this is not quite correct. The strategies attributed to him are what are actually considered, and these strategies are recorded and exist whether or not he himself did. Whether some successful leader named Napoleon actually developed these strategies, or whether they are merely attributed in texts to some figurehead by an unknown author, does not actually have any bearing on their validity, for this can be determined entirely by logical analysis and experimental verification of these assertions. If they work and are relevant to modern warfare, we use them, if not, we don't. It would be nice to know for certain whether Napoleon existed or not, but if we didn't and couldn't then it wouldn't be a problem.
This is the key thing to remember about Jesus. We should be concerned not with the person's historicity, but with the verifiable validity of the assertions attributed to him. Many are unverifiable, and thus should not be credited by a rational mind.
Some may make the argument that he did exist, and having actually been in his presence, touched the nail holes in his hands (as the story asserts), etc. then this did, of course constitute scientific verification of his existence. True, but only for those present at the time. Reading accounts of their own verification of the truth, 2000 years ago, does not constitute verification for us today. Unless we ourselves can perform similar tests, then it is not verifiable today, even if it once was, and should not be believed. This is the very crux, if you'll pardon the word, of modern science and rationality.
That's just the way rationality works, and if an omnipotent god does exist, surely he would have been bright enough to arrange for verification to be available to every following generation rather than just the one coinciding with the actual events.
