Moral relativism, the idea that there are no absolute moral principles, that what is "right" depends on the values of the time or the culture in which you live, is usually the refuge of left-wing ideologues who confuse it for cross-cultural tolerance.

It's not usually adopted by authoritarian WASPs who have built their careers and reputations on upholding the strictest moral standards, or at least, appearing to.

Men like Paterson, part-governors, part-gods, don't usually go in for that sort of undergraduate nonsense.

And yet that was what Paterson told the Royal Commission this week, in an effort to excuse his historical failure to protect his students from paedophiles in their midst.

'The times were very much different then," he said.

"We judged people ourselves."

This is an idea we hear reasonably often – that we should evaluate people according to the historical standards of the time, not by present-day mores.

To an extent, we all accept it. It is the reason why we can appreciate the sophistication of Roman culture while still acknowledging that gladiatorial combat was barbaric. It is the reason Americans can revere founding father Thomas Jefferson even though he was a slave owner (although one school of thought is that he was just a straight-up hypocrite). It is a way for us to understand the past.

But applied to a privileged upper north shore grammar school in the '80s and '90s? I don't think so.

In the case of Knox, and Paterson, and the pattern of cover-up and neglect that has emerged from this week's evidence at the Royal Commission into Child Sex Abuse, the idea that different historical attitudes towards child-abuse applied, is bunkum.

Paterson admitted as much himself this week, albeit inadvertently. He told the commission that 1989, when a boy came to tell him that a teacher, Damien Vance, had groped and propositioned him, Paterson did not think to call the police.

"I'm not aware that was a matter for the police or a crime," he said.

Only seven years later, in 1996, a police investigator approached him asking for documentary evidence of six Knox teachers who were thought to have abused boys.

Presumably at that stage, Paterson twigged that child-groping might be a crime – police don't tend to concern themselves otherwise. Nonetheless he withheld evidence about the men from the police, he admitted this week.

I was a high school student in the early to mid-90s, not so long after some of the reported events took place. I attended North Sydney Girls' High, about 20 kilometres south down the Pacific Highway from Knox. As an all-girls school, we occasionally attracted predatory attention. We were given instructions on how to deal with flashers.

The favourite lunch spot of my little gang was a perch at the edge of the school grounds, overlooking the footpath and the main road. We liked to watch the passers-by and give teenage commentary on them.

One lunchtime an unassuming man walked past and placed on the wall, directly in front of us, an exercise book. He walked on. We opened the book to find it was full of hardcore pornographic images, lovingly pasted in and accompanied by painstakingly executed hand-written commentary. It was a compendium of the vile sexual fantasies of a man who got off, I assume, on the thought his hand-crafted book would one day be squealed over by short-skirted schoolgirls.

We took the book immediately to the headmistress, who called the police. They arrived within an hour and seized the book as evidence. That was in either 1990 or 1991 and we were about 13 years old. To say there was no awareness back then of paedophilia and the danger posed by "low-spectrum" behaviours like groping or porn-scrapbooking is nonsense.

The heart-breaking thing about the Knox abuse victims is that they had exactly the same instinct as my friends and I did.

Tell a responsible adult. Tell the boss of the school. He will take care of things. He will take care of me.

In our case, our trust was fulfilled. In their case, it wasn't.

As an adult it's easy to forget the God-like authority the school principal holds in the childish consciousness. I imagine this perceived power is heightened at a strict private school where reputation is paramount and there is an emphasis on moral instruction. The presence of the headmaster or headmistress looms large and omnipotent. It is inescapable.

What we realised this week was that Paterson appeared to take himself at the God-like estimation of his child pupils. He thought he was the ultimate authority, and it didn't occur to him to call in police. He had the power to airbrush from history the misdeeds of paedophiles, giving at least one abusive teacher a glowing reference and sending him on to other schools, and other pupils. He withheld information from the police.

The present culture of revelation and transparency around sex abuse, which led to the establishment of the Royal Commission and which has been so well served by it, is certainly a new thing.

And what we have learnt, from story after story of bone-chilling abuse, is something similar to Hannah Arendt's great observation about the Nazis and the banality of their evil.

Child sex abuse is so prevalent, and so much a part of humanity, it will probably always take place. There will always be evil people who abuse children.

But what has been fascinating to observe is the way churches, schools, orphanages, families, and whole cultures can collude to create an atmosphere that is perfectly conducive to child-abusing. Every member of those institutions is not evil. But that doesn't mean we should historically excuse them either.

We should absolutely judge history, especially recent history, by the prevailing moral standards of today. It is only through that prism that we can learn from it.

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