By now surely everyone knows the case of the eight men convicted of picking vulnerable underage girls off the streets, then plying them with drink and drugs before having sex with them. A shocking story. But maybe you haven't heard. Because these sex assaults did not take place in Rochdale, where a similar story led the news for days in May, but in Derby earlier this month. Fifteen girls aged 13 to 15, many of them in care, were preyed on by the men. And though they were not working as a gang, their methods were similar – often targeting children in care and luring them with, among other things, cuddly toys. But this time, of the eight predators, seven were white, not Asian. And the story made barely a ripple in the national media.

Of the daily papers, only the Guardian and the Times reported it. There was no commentary anywhere on how these crimes shine a light on British culture, or how middle-aged white men have to confront the deep flaws in their religious and ethnic identity. Yet that's exactly what played out following the conviction in May of the "Asian sex gang" in Rochdale, which made the front page of every national newspaper. Though analysis of the case focused on how big a factor was race, religion and culture, the unreported story is of how politicians and the media have created a new racial scapegoat. In fact, if anyone wants to study how racism begins, and creeps into the consciousness of an entire nation, they need look no further.

Imagine you were living in a town of 20,000 people – the size of, say, Penzance in Cornwall – and one day it was discovered that one of its residents had been involved in a sex crime. Would it be reasonable to say that the whole town had a cultural problem, that it needed to address the scourge – that anyone not doing so was part of a "conspiracy of silence"? But the intense interest in the Rochdale story arose from a January 2011 Times "scoop" that was based on the conviction of at most 50 British Pakistanis out of a total UK population of 1.2 million, just one in 24,000: one person per Penzance.

Make no mistake, the Rochdale crimes were vile, and those convicted deserve every year of their sentences. But where, amid all the commentary, was the evidence that this is a racial issue; that there's something inherently perverted about Muslim or Asian culture?

Even the Child Protection and Online Protection Centre (Ceop), which has also studied potential offenders who have not been convicted, has only identified 41 Asian gangs (of 230 in total) and 240 Asian individuals – and they are spread across the country. But, despite this, a new stereotype has taken hold: that a significant proportion of Asian men are groomers (and the rest of their communities know of it and keep silent).

But if it really is an "Asian" thing, how come Indians don't do it? If it's a "Pakistani" thing, how come an Afghan was convicted in the Rochdale case? And if it's a "Muslim" thing, how come it doesn't seem to involve anyone of African or Middle Eastern origin? The standard response to anyone who questions this is: face the facts, all those convicted in Rochdale were Muslim. Well, if one case is enough to make such a generalisation, how about if all the members of a gang of armed robbers were white; or cybercriminals; or child traffickers? (All three of these have happened.) Would we be so keen to "face the facts" and make it a problem the whole white community has to deal with? Would we have articles examining what it is about Britishness or Christianity or Europeanness, that makes people so capable of such things?

In fact, Penzance had not just one paedophile, but a gang of four. They abused 28 girls, some as young as five, and were finally convicted two years ago. All were white. And last month, at a home affairs select committee, deputy children's commissioner Sue Berelowitz quoted a police officer who had told her that "there isn't a town, village or hamlet in which children are not being sexually exploited".

Whatever the case, we know that abuse of white girls is not a cultural or religious issue because there is no longstanding history of it taking place in Asia or the Muslim world.

How did middle-aged Asian men from tight-knit communities even come into contact with white teenage girls in Rochdale? The main cultural relevance in this story is that vulnerable, often disturbed, young girls, regularly out late at night, often end up in late-closing restaurants and minicab offices, staffed almost exclusively by men. After a while, relationships build up, with the men offering free lifts and/or food. For those with a predatory instinct, sexual exploitation is an easy next step. This is an issue of what men can do when away from their own families and in a position of power over badly damaged young people.

It's a story repeated across Britain, by white and other ethnic groups: where the opportunity arises, some men will take advantage. The precise method, and whether it's an individual or group crime, depends on the particular setting – be they priests, youth workers or networks on the web.

Despite all we know about racism, genocide and ethnic cleansing, the Rochdale case showed how shockingly easy it is to demonise a community. Before long, the wider public will believe the problem is endemic within that race/religion, and that anyone within that group who rebuts the claims is denying this basic truth. Normally, one would expect a counter-argument to force its way into the discussion. But in this case the crimes were so horrific that right-thinking people were naturally wary of being seen to condone them. In fact, the reason I am writing this is that I am neither Asian nor Muslim nor Pakistani, so I cannot be accused of being in denial or trying to hide a painful truth. But I am black, and I know how racism works; and, more than that, I have a background in maths and science, so I know you can't extrapolate a tiny, flawed set of data and use it to make a sweeping generalisation.

I am also certain that, if the tables were turned and the victims were Asian or Muslim, we would have been subjected to equally skewed "expert" commentary asking: what is wrong with how Muslims raise girls? Why are so many of them on the streets at night? Shouldn't the community face up to its shocking moral breakdown?

While our media continue to exclude minority voices in general, such lazy racial generalisations are likely to continue. Even the story of a single Asian man acting alone in a sex case made the headlines. As in Derby this month, countless similar cases involving white men go unreported.

We have been here before, of course: in the 1950s, West Indian men were labelled pimps, luring innocent young white girls into prostitution. By the 1970s and 80s they were vilified as muggers and looters. And two years ago, Channel 4 ran stories, again based on a tiny set of data, claiming there was an endemic culture of gang rape in black communities. The victims weren't white, though, so media interest soon faded. It seems that these stories need to strike terror in the heart of white people for them to really take off.

What is also at play here is the inability of people, when learning about a different culture or race, to distinguish between the aberrations of a tiny minority within that group, and the normal behaviour of a significant section. Some examples are small in number but can be the tip of a much wider problem: eg, knife crime, which is literally the sharp end of a host of problems affecting black communities ranging from family breakdown, to poverty, to low school achievement and social exclusion.

But in Asia, Pakistan or Islam there is no culture of grooming or sex abuse – any more than there is anywhere else in the world – so the tiny number of cases have no cultural significance. Which means those who believe it, or perpetuate it, are succumbing to racism, much as they may protest. Exactly the same mistake was made after 9/11, when the actions of a tiny number of fanatics were used to cast aspersions against a 1.5 billion-strong community worldwide. Motives were questioned: are you with us or the terrorists? How fundamental are your beliefs? Can we trust you?

Imagine if, after Anders Breivik's carnage in Norway last year, which he claimed to be in defence of the Christian world, British people were repeatedly asked whether they supported him? Lumped together in the same white religious group as the killer and constantly told they must renounce him, or explain why we should believe that their type of Christianity – even if they were non-believers – is different from his. "It's nothing to do with me", most people would say. But somehow that answer was never good enough when given by Muslims over al-Qaida. And this hectoring was self-defeating because it caused only greater alienaton and resentment towards the west and, in particular, its foreign policies.

Ultimately, the urge to vilify groups of whom we know little may be very human, and helps us bond with those we feel are "like us". But if we are going to deal with the world as it is, and not as a cosy fantasyland where our group is racially and culturally supreme, we have to recognise when sweeping statements are false.

And if we truly care about the sexual exploitation of girls, we need to know that we must look at all communities, across the whole country, and not just at those that play to a smug sense of superiority about ourselves.