Tempting though it is to try to score this fight, I'm going to pass, and instead comment on a paper by philosopher Stephen Law that also addresses the existence question. (There's a shorter version at Secular Outpost.) The core idea is this premise:
(P2) Where testimony/documents weave together a narrative that combines mundane claims with a significant proportion of extraordinary claims, and there is good reason to be sceptical about those extraordinary claims, then there is good reason to be sceptical about the mundane claims, at least until we possess good independent evidence of their truth.
He concludes that
The contamination principle, P2, is a prima facie plausible principle that, in conjunction with other prima face plausible premises, delivers the conclusion that, in the absence of good independent evidence for the existence of an historical Jesus, we are justified in remaining sceptical about the existence of such a person.
Now, if Law were simply saying that we should be initially sceptical, before a detailed historical investigation, of any and all claims about Jesus that we find in the New Testament, then he is not saying anything new. NT scholars have subscribed to this view for many decades, and any competent scholar knows that they must fight strenuously for any statement to be taken as more or less accurate reflection of something Jesus actually said. (See, for example, J.D. Crossan's book The Historical Jesus to find out how this is done.)
But this is not what Law is saying. Rather, he thinks that, even after a detailed historical investigation, the very nature of the evidence means that no reliable conclusion can be obtained. He specifically considers the usual criteria that NT scholars use to evaluate individual sayings and acts, and declares them insufficient to establish a conclusion, even about basic facts like whether Jesus lived.
Not, mind you, that he has carried out such a detailed investigation and come to a negative conclusion. No, he claims that regardless of what comes out of a detailed investigation, the philosophical principles he lays out preclude a positive result.
In effect, he is saying that philosophy trumps history. This bothers me, in part because I have recently been involved in a discussion over on Victor Reppert's blog where some folks are claiming that philosophy trumps science.
But let's return to Law's "contamination principle" (P2). As many folks have pointed out, most ancient sources from the time of Jesus have supernatural episodes interlarded with portions that are generally agreed by historians to be reliable history. If we are not to reject all such sources, we must set some kind of a cut-off point: 25% miracles, dump the whole thing; 24% miracles, OK to use it. Or whatever.
Now, suppose we have a document that contains 30% miracle stories. By Law's criterion, we should dump it. But suppose that detailed historical investigation reveals that this document is actually a composite document, written by two different people at two different times. (And possibly combined into a single document by a third person, or one of the two original authors: I don't think the details matter.) And suppose that one of the source documents doesn't contain any miracles at all, while the other source contains a high percentage.
Now we have a contradiction: the contamination principle demands that we dump the document as a whole, but it allows us to retain the source document.
So it seems to me that Law's P2 cannot do what he wants it to do. It cannot circumvent the detailed historical investigation and declare it invalid. A detailed confrontation with the actual historical evidence is the only way to derive valid historical conclusions.
And that's what historians (and NT scholars) do.