I think that it is necessary to at least acknowledge even extreme Catesian skepticism. We must acknowledge the limits of epistemology to be fully honest. At the same time we should not abandon all beliefs, the question is which ones are worth keeping, and why. Clearly our belief in the external world as we percieve it (allowing for known errors) is somethign that we must at least pragmatically accept. But much beyond that is - and should be - open to question.
With regard to the existence of Jesus I have to say that I see no reason to believe that the gospels are complete fictions and that there was no historical person behind them. At the same time we must acknowledge that the Gospels are second-hand accounts (maybe excepting the majority of John), certainly partisan in being Christian documents and quite probably partisan even within the Christian movement. If we applied the ordinary standards of rational inquiry to them we should be sure that the Gospels contain many inaccuracies. They are as much - or more - about the Jesus the writers wanted to believe in as they are about any historical person.
Does this disturb you ? Maybe it should. But it is a fact that needs to be recognised - especially by believers.