In his Easter sermon, the Archbishop of Canterbury, Dr Rowan Williams, complains of the regular flurry of conspiracy theories and sensational new discoveries which supposedly threaten the church's very foundations. This year's examples are the Gospel of Judas and the renewed excitement over the Da Vinci Code after the recent copyright trial and in anticipation of the forthcoming film of the book.

The archbishop goes on to complain that people are disinclined to accept the traditional Christian story because it comes from the church, an establishment body of authority and power, in an age when the establishment is often viewed with suspicion.

Dr Williams is right to be dismayed by both phenomena. Our populist, instant excitement-seeking, culture and media have written off with monotonous regularity Christianity, western culture, Capitalism, the monarchy and numerous other things which are still with us. Perfectly good official advice goes unheeded because a sensationalist scare story carries more weight. As a result we get problems such as a rise in the incidence of measles because too many parents have refused to allow their children to receive the MMR vaccine, on the basis of media misrepresentations of a single uncorroborated and later partially-retracted piece of scientific research.

As Dr Williams says, people don't trust power, and the church is traditionally part of this country's power structure. The lack of trust is not entirely without foundation, though - power tends to corrupt. But even if that were not the case, we must be careful not to go to the other extreme, and suggest that establishment bodies are right simply because the majority of objections to them stem from an irrational suspicion of power. Any claims, whether from sensationalist book-writers, politicians, experts or archbishops, should stand or fall on their intrinsic merits.

Fortunately, perhaps, the archbishop does move on from his complaints to discuss the merits of the conventional Christian message. He says we have to strip away the "accumulated lumber of 2,000 years of rather uneven Christian witness and try to let the event [the resurrection] be present in its first, disturbing, intimacy", and goes on to explain that the Church does not exist in order to arbitrarily lay down what people believe or to remember a dead leader. According to Dr Williams, the Bible is not the "authorized code of a society managed by priests and preachers for their private purposes." Rather, the church exists "so that people in this and every century may encounter Jesus of Nazareth as a living contemporary" whom we are invited to meet. The Bible is a set of human words ... "with divine energy behind them".

He then declares that the sceptic will say "but why on Earth should I believe that?" Yes, we sceptics will as ask that - why should we believe it? Why should we believe that a man for whom there is no first-hand evidence from his own lifetime not only lived (which is a possibility) but lives still in some form which can be encountered by people today (which is stretching sceptical credulity to breaking point)? Dr Williams advances two arguments.

First, "it was written by people who, by writing what they did and believing what they did, were making themselves, in the world's terms, less powerful, not more".

Leaving aside the question of whether this is true (was Paul the leader of a growing religious community throughout the Mediterranean less powerful than Saul the Palestinian tentmaker?), what exactly is Dr Williams suggesting here? That no person or group would, or could, put themselves in a position where they lose power unless the reason for doing so was the gospel truth? Is he suggesting that people never put themselves into minority positions, or risk persecution, for beliefs which they may sincerely believe, but which turn out to be untrue? Are the followers of what is now orthodox Christianity the only people to have knowingly made themselves less powerful because of their beliefs?

The answers to these questions seem very obvious to me. Many, many peoples have lost power and accepted suffering for their beliefs, principles and long-term aspirations; and many of those beliefs directly contradict the standard Christian "truth". For thousands of years, Jews could have ended their suffering and marginalisation by turning away from their Jewish beliefs and culture, but they held on to their faith, even in the face of the Holocaust. Is that a reason to believe the tenets of Judaism, including their insistence that Jesus was not the Messiah? Within Christianity, numerous "heretical" groups have sprung up knowing that they risked life, limb and power for their beliefs, many of which are at odds with the faith that Dr Williams espouses. Perhaps even the author of the Gospel of Judas was taking such a risk! Since history is littered with the remains of powerless and persecuted minority groups and religious communities, each sincerely convinced of the truth of their belief, and since those beliefs are mutually exclusive, it is a simple matter of logic to conclude that such power-loss, such suffering, proves nothing at all about the veracity of the beliefs themselves. It proves only their power to take hold of people's minds and emotions.

Dr William's second argument is that "the New Testament was written by people who were still trying to find a language that would catch up with a reality bigger than they expected". This is a circular argument. The sceptic is asking "why should we believe that what these people believed to be the truth was actually the truth?, and the archbishop's answer is to cite the very beliefs, or "reality", in question. In what way does a struggle to express an idea prove the veracity of the idea itself? It doesn't.

Nothing in the remainder of Dr William's message provides any more arguments in answer to the question of "why should we believe it?". He states more of the beliefs themselves as if they are proven fact, and cites the moving stories of people who's actions have been based on their acceptance of those beliefs.

Both of the archbishop's arguments may present evidence of the depth and sincerity of the beliefs which existed in the minds of early (and modern) Christians, but they don't begin to address the question of whether or not the beliefs themselves are true. They don't begin to explain why we should believe the mainstream church's Christianity, as opposed to the beliefs of others who have suffered and struggled in similar ways, or, indeed, why we should believe any such faith-based belief system. If he is serious about answering the sceptics' question, then he needs to address the concerns of sceptics themselves : the need for evidence of the events on which his faith is based, not merely evidence of others' belief in those events. I assume that he is knowledgable enough to know that his answers are not answers at all (to a sceptic), so why bother?