There is only one conceivable reaction to the fast-spreading crisis in the Catholic church: horror. Only the most virulent anti-papist could ever have quite envisaged the scale of child abuse and the doggedness of the church's desire to stifle scandal. The rest of us are astonished and appalled. Quite rightly, Angela Merkel saw fit to intervene. After decades – perhaps we should rather be referring to centuries – of obfuscation, the Catholic church has to be called to account for what has happened.

Since abuse allegations first emerged in the early 90s in the UK and Ireland, the denials, both those of officials and those which ordinary Catholics told themselves, have shifted several times. Initially the church authorities declared it was just a few bad apples, but last summer the Ryan report exposed decades of systematic abuse of thousands of children in Ireland. Another line of defence was that it was a particular Anglophone problem with roots in Ireland's excessively deferential Catholic culture, which had then been exported to the US and Australia.

Now this explanation is falling apart as abuse allegations emerge across Europe in Germany, the Netherlands, Switzerland and Italy. Last summer, scandal erupted in the Hispanophone media when stories in Spain and Mexico alleged that Marcial Maciel, the Mexican founder of a religious order, the Legion of Christ, and much favoured by Pope John Paul II, was found to have fathered several children. After allegations of child abuse, the entire order – with institutions in several Latin American countries – is now under investigation by the Vatican.

Oxford church historian Diarmaid MacCulloch argues that this is as he predicted in his book on the Reformation. Back in 2003 he warned that when allegations of child abuse spread to non-Anglophone countries, the results would be "catastrophic" for the church. Old cultures of deference have succeeded in repressing the truth for longer, but now even they are disintegrating.

Another defence put forward by many loyal Catholics has been that the incidence of child abuse by religious figures has been broadly in line with secular society; but even this argument looks increasingly unsustainable. The current issue of the Catholic weekly, the Tablet, carries a thoughtful article by the head of Berlin's Institute of Sexology and Sexual Medicine which acknowledges that the church's celibacy requirement may have appealed – misleadingly appearing to offer a solution – to paedophiles' conflicted sexuality. While the debate about disproportion continues, what is increasingly clear is that the church's determination to preserve its institutional power and authority repeatedly involved suppressing the truth – even when that put children at further risk.

This is utterly bewildering to faithful Catholics raised to revere and trust the institution and its priests. But it is equally disturbing for those vaguely anticlerical Catholics (yes, they exist in surprising numbers) who have tended to regard priests as a necessary embarrassment, an unavoidable irritant whom they did their best to avoid while still finding great inspiration in the faith. The latter position is hard now to sustain; what the crisis starkly exposes is that one of the defining characteristics of Roman Catholicism has been the central role of the priest, and that it is fundamentally flawed for two reasons.

Both are rooted in the medieval theology that when a man becomes a priest, his nature is fundamentally changed – he becomes a different sort of human being. As such, he firstly no longer has the normal human sexual needs; and secondly, he has a particular authority which deserves (and expects) unquestioning respect. Both assumptions are still widely evident in the Catholic church today. Many priests have an extraordinarily inflated view of their position – there are exceptions, but they are rare.

Priests belong to a church hierarchy which owes much to the Roman empire. The pattern of obedience to superior authority ensured that there was no system of the checks and balance essential to prevent abuse of power. Nor has there been much tolerance for challenge and debate; an entire institutional culture has increasingly been dominated by the imperative of self-preservation. The commitment to the prestige and authority of the institution has been paramount – and too often that has been at the cost of individual lives. Modernity has only exacerbated these tendencies; the Catholic church became more centralised around a strengthened papacy in the 19th century – at exactly the same time as European states were becoming more democratic. The result has been an astonishingly successful global institution in some respects, acquiring millions of new adherents over the course of the 20th century in Africa and Asia. But the necessary impetus for reform has been crippled.

"This is nemesis. An organisation consumed by hubris was bound to get its comeuppance," declares MacCulloch, presenter of the BBC's recent History of Christianity. "Are we about to see another reformation as the angry faithful reject how they have been conned?"

Perhaps MacCulloch is too hopeful; more likely than another reformation is a less dramatic emptying of the European Catholic churches. The crisis simply accelerates what is already happening: the drift away from a model of religious experience which younger generations find increasingly unintelligible. Despite all the talk in Ireland and elsewhere of inquiries to ascertain the truth and "rebuild confidence in the church", such initiatives are very unlikely to achieve that outcome. Inquiries prompt more lurid headlines as they expose further the scale and detail of the abuse. They are necessary and important, but they will not save the Catholic church.

The church's loss of moral authority is only a part of a bigger picture. Financial ruin provoked by compensation claims is another – as the Boston archdiocese well knows. And one of the most acute and pressing consequences of the abuse scandal is that it exacerbates the problem that the church is running out of priests as vocations collapse; a model of religious practice based on the mass will be unsustainable in many parts of Europe within a decade or two.

There will be plenty celebrating the Catholic church's plight, and it is hard not to agree in some part with MacCulloch, that hubris has played a huge part in this institution's history and its current crisis. But it is also important to acknowledge that this is more tragedy than anything else. For the victims, their families, their congregations – many of whom see no cause for celebration despite their need for truth – and for those causes on which the church has proved a trenchant champion, stirring lazy consciences on the arms race, global inequality and capitalist excess.