I’ve been fascinated by Horst Mahler – who, it has just emerged, may have been a Stasi informant in the 1960s – since I wrote a profile of him for The Times in 2003. The son of a Nazi, he became a socialist lawyer in the 1960s and represented leaders of the West German student movement such as Rudi Dutschke. After its collapse, he founded the Red Army Faction (RAF), the West German left-wing terrorist group, and spent the whole of the 1970s in prison until he was released with the help of another young left-wing lawyer named Gerhard Schröder. Just after Schröder became Germany’s Social Democrat chancellor in 1998, Mahler became a neo-Nazi and represented the far-right NPD. He is now in prison serving a seven-year sentence for denying the Holocaust – a criminal offence in Germany. But what, if anything, does his strange political journey tell us?

The key question about Mahler – who is also one of the central characters in my book, Utopia or Auschwitz – is whether he should be seen as an anomaly or representative of a wider phenomenon. As David Aaronovitch put it at the launch of the book in London in November 2009, are we talking about an ideology or a pathology? Many on the left in general and former members of the student movement in particular dismiss Mahler as simply crazy. To some on the right, however, Mahler’s strange political journey is actually an illustration of the proximity of far-left and far-right ideology – the idea that “les extrêmes se touchent”. The best answer I have to Aaronovitch’s question is that the thinking of the 1968 generation – of which Mahler is not representative but nevertheless illustrative – was the product of a complicated mixture of both ideology and pathology.

The key to understanding Germany’s 1968 generation, it seems to me, is the Nazi past. The Achtundsechziger were the children of the generation of the Germans who were responsible for the Holocaust – what they called the “Auschwitz generation”. Many of them grew up with an acute sense of being the “children of murderers”, as Rainer Langhans, a key figure in Kommune 1 (a West Berlin commune that played a key role in the student movement), put it when I interviewed him for the book. The West German student movement can therefore be understood as a kind of ex post facto resistance against Nazism. The sympathy of some of its members for the “anti-fascist” GDR should also be seen against this background. Yet although it thought in terms of “resistance”, it also had nationalist and anti-Semitic undercurrents within in. In other words, it was not simply a left-wing movement but rather a mixture of left-wing and right-wing ideas.

Mahler is the most extreme – but not the only – example of this phenomenon. As I told the Guardian last week when it emerged that he may have informed for the Stasi, his whole life has been a struggle with the Nazi past. In that context, it seems to me that his far-right turn can be understood in pathological terms as a kind of posthumous reconciliation with his Nazi father. “We have to straighten out our relationship with our parents,” he wrote in a book published together with another German neo-Nazi, Franz Schönhuber, in 2000. Another striking example is Bernward Vesper, Gudrun Ensslin’s husband. Vesper’s father was the Nazi poet Will Vesper, whom he both hated and tried to rehabilitate together with Ensslin before she left him for Andreas Baader, the central figure in the RAF. (The story of the bizarre love triangle between Baader, Ensslin and Vesper is the subject a good movie that came out in Germany earlier this year, Wer wenn nicht wir).

At the same time, however, it seems to me impossible to understand the 1968 generation completely in pathological terms. Rather, it inherited and developed elements of a longer line of anti-liberal political thought in Germany – what Adorno, in his essay “Was bedeutet: Aufarbeitung der Vergangenheit” (“What is meant by the working through the past?”), called “the anti-civilisational, anti-Western undercurrent of the German tradition”. This undercurrent is intimately connected to the history of German nationalism, which emerged in opposition to the French revolution and the Enlightenment ideas it represented in the early nineteenth century. It influenced both right-wing and left-wing critiques of capitalism in the twentieth century and culminated in Nazism but continues to be of relevance to contemporary debates about Germany and the West. What Mahler ultimately illustrates, it seems to me, is that in some ways the most interesting fault line in German intellectual history is not between left and right but between liberalism and anti-liberalism.