@Olivier5,
Well, astronomers, cosmologists, etc, have worked out a model of the evolution of the universe back to within milliseconds after the BB. Of course, it is incomplete, but I don't know of any serious challenge to it as a whole, seeing as how even the developments with dark matter and energy didn't necessitate a new model. There's cosmic background radiation, radioactive decay and a host of other observations and experiments that support the BBT. (
http://www-donut.fnal.gov/web_pages/standardmodelpg/TheStandardModel.html ) If it turned out that there was no BB, the whole Standard Model would have to be thrown out or revised to the point that it would be unrecognizeable. As far as I know, even string theory or superstring theory would be an expansion of the existing Standard Model, not a challenge to it.
Compared to what would happen if it turned out that there was no historical Jesus. Yes, it would have widespread social, religious and political implications, but it wouldn't overturn the way professional history is done, would it? And...what is the actual, physical evidence that such a person actually existed?
In terms of physical evidence, I don't think there's more for the existence of Jesus than for Lao Tzu. Both are confined to ancient texts. Yet the existence of a historical Lao Tzu is strongly suspect in the eyes of western scholars, less so by Chinese historicans, if I'm not mistaken. I suspect, but haven't made any effort to prove, that cultural indoctrination has a significant influence on which historical figures, shrouded by the mists of time and scanty evidence, are given more or less plausibility. Just a passing observation: there's a whole lot more riding - in global political and economic terms - on the existence of Jesus than of Lao Tzu.
As for me, I suspend judgement on both accounts, ie, both the Jesus question and the BBT/Standard Model theory. I don't see where, as a layman, having an opinion or belief one way or the other is useful or prudent. But I do see value in being able to weigh the relative strengths of arguments, and I don't see the Jesus argument to be nearly as robust as the BBT/Standard Model theory.
As always, I could be wrong.