‘You turned the issue on its head,” someone said to me after I gave a talk on identity politics in Melbourne last week. “I’ve never thought of it that way round.” It always was on its head, I said to her. It’s just that we’ve never noticed.

I’ve been in Australia over the past week talking, among other things, about the politics of identity. The issue has, in the wake of the Christchurch mosque massacres, acquired new resonance. The gunman, who has been charged in a New Zealand court with 50 counts of murder, was Australian. It has led to much soul searching about white nationalism and its roots and about the role of mainstream media and politics in fuelling hatred.

There is, though, in Australia as elsewhere, a strange disjuncture in such discussions. There is a heated debate about identity politics, which focuses primarily on the left, and on whether it makes sense to adopt such politics. There is an equally heated, but separate, debate about white identity and white nationalism.

Rarely, though, have the two debates been linked or the relationship between the identity politics of the left and that of the right been explored at any great depth. Which is why when you do place the two debates within the same frame, it can feel to some as if the issue has been turned on its head.

One of the consequences of the bifurcated debate is historical amnesia about the origins of identity politics. Most people imagine that its roots are on the left. In fact, they lie on the reactionary right, in the counter-Enlightenment of the late 18th century. It wasn’t then called the politics of identity. It was called racism. It is, however, in the concept of race – the insistence that humans are divided into a number of essential groups, and that one’s group identity determines one’s moral and social place in the world – that we find the original politics of identity, out of which ideas of white superiority emerged.

Where reactionaries adopted an identitarian outlook, radicals challenged inequality and oppression in the name of universal rights. From anti-colonial struggles to the movements for women’s suffrage to the battles for gay rights, the great progressive movements that have shaped the modern world were a challenge to the politics of identity, to the claim that an individual’s race or gender or sexuality should define their rights, or their place in a social hierarchy.

Only after the Second World War did the relationship between left, right and identity change. In the wake of Nazism and the Holocaust, overt racism became less acceptable. The old politics of identity faded, but a new form emerged – identity politics as a weapon wielded not in the name of racism but to confront oppression and to challenge inequality.

Faced with a left often indifferent to their plight, black people, women, gay people and others transformed the political landscape by placing their own experiences of oppression at the heart of new social movements. But what began as struggles against oppression and for social change transformed over time into demands for cultural recognition by myriad social groups. The social movements of the 1960s gave way to the identity politics of the 21st century.

The nadir of this process came with the demand that white people, too, be culturally “recognised”. Over the past decade, in the face of populist hostility to immigration, especially Muslim immigration, many mainstream commentators began arguing that white people should be able to assert what the political scientist Eric Kaufmann has called their “racial self-interest”.

The identitarians of the far right seized on the opportunity to legitimise their once-toxic brand, reclaiming their original heritage. Racism became rebranded as white identity politics. And, having spent decades promoting the politics of identity, the left found itself paralysed in the face of this shift.

There is no straightforward equivalence between the identity politics of the left and that of the far right. The former emerged from the decay of genuine movements for social change and betterment; the latter is the product of a vicious racist outlook, one of the most degenerate expressions of which came in Christchurch.

It is, nevertheless, a measure of contemporary confusion that so many on the left imagine that an approach that draws upon ideas of group identity that lie at the heart of racial thinking can challenge inequality and injustice. Understanding the roots of identity politics, and turning conventional perception on its head, has rarely seemed such an urgent task.

• Kenan Malik is an Observer columnist