Until his death in the early 1990s, my grandad was a committed Nazi. Most of his elder brothers died in one night at the battle of the Hartmannsweilerkopf in the first world war. In a bitterly traumatised interwar Germany, defined by hatred against foreigners, Jews and democracy as well as delusions of national grandeur, he was unemployed for most of the 1920s. He joined the Nazi party early, and volunteered to fight in 1940. He became a staff sergeant in the Wehrmacht and led a so-called “anti-partisan” unit on the eastern front, and participated in the capture of Kiev.

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We believe he took part in the September 1941 Babi Yar massacre, in which more than 33,000 Jewish inhabitants of Kiev were shot. Until his death he would rant about Jews, the French and the perfidious Albion. He never left the country again and he’d be in a near panic when coming close to a border.

My maternal grandfather, meanwhile, was a teacher from Duisburg. When he went to war he left his wife, two children, his camera, his library and all hope of survival behind. He survived three years on the eastern front but never played music again, never took up photography again. He was a broken man. While he was away, my grandmother remained in Duisburg. She was “bombed out” three times, meaning that her flat or house got a direct hit. Until her death, the sound of sirens would send her into a panic.

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My father was born in 1944. Growing up in a postwar Nazi household, he started reading early and joined the Scouts. He discovered the ideas of democracy and civil rights, and became a Social Democrat with a boiling rage against anything even remotely rightwing. My mother, born in 1947, met him in 1968 at university. In a West Germany still defined by large numbers of unrepentant Nazis, participating in anti-Nazi protests became their defining political experience. They built a home for five children, full of music, books, art and a clear understanding that being German came with a responsibility to be very careful with your politics.

During my childhood I was evacuated four times because of unexploded second world war bombs. Since then I’ve been evacuated twice for the same reason. During our school years we visited Verdun and Bergen-Belsen. We read not just Goethe, Schiller and Mann, but also Anne Frank’s diary and Eugen Kogon’s Der SS-Staat. We thought our teachers concentrated a bit too much on the Third Reich sometimes.

When the Berlin Wall came down in 1989, my parents woke all the kids. We sat in front of the TV sipping our first champagne and watching our parents cry. My father told me that this was the day the second world war truly ended, and that our European friends made it possible.

Growing up, all five of us were sent abroad multiple times. We learned several languages and were encouraged to travel far and wide. My best friend is a Jew from Manhattan living in Norway. Every time I visit her I cherish the thought of my grandad turning in his grave. A united Europe is our legacy. The EU is a champion of peace and prosperity, not an economic project. While Nato ensured the absence of military conflict in western Europe, the EU and its predecessors actually built the peace, integrating European nations into a peaceful coalition of cultures bound by a common set of values and defined by a common future.

Facebook Twitter Pinterest ‘When the Berlin Wall came down in 1989 we sat in front of the TV sipping our first champagne and watching our parents cry.’ Photograph: Lionel Cironneau/Associated Press

Watching my father play with my nephew, I am witness to the first three consecutive generations of Germans living in uninterrupted peace. Ever. Nobody is going to endanger that unopposed. Looking at my grandfather and my father, the most striking difference in their formative experiences is defined by the narrative surrounding their sense of national identity. On the one hand, self-pitying revanchist nationalism, based on the “stab in the back” myth and absolving its leaders and the nation from any responsibility to face the consequences of their actions; on the other, determined, hard-fought realism, based on the acceptance of responsibility and the acknowledgment of crimes, embracing liberalism and democracy as the core of one’s identity.

That modern national identity is not based on a guilt complex, but on the understanding that identifying as German requires an acknowledgment of all aspects of our past. Identifying proudly with football World Cup victories is nonsensical without careful consideration of our warmongering history. Likewise, a sense of responsibility for those crimes is meaningful only when combined with a proud identification with accomplishments such as Germany’s participation in the creation of the EU.

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The EU today is the hard-fought culmination of decades of peace-building and political integration. It’s far from perfect, but it remains the only successful format of democratic, international integration. In a globalised world, it enhances national sovereignty through combining its members’ economic and political power, while guaranteeing its citizens unparalleled degrees of freedom and stability.

In recent years, a wave of far-right parties has washed over the EU’s member states, from the Sweden Democrats to Germany’s AfD and the Rassemblement National in France. And I realise that school classes about the rise of the Third Reich may not have been overdone after all.

In the UK this surge, combined with decades of nearly unopposed anti-EU rhetoric, led to Brexit. The post-fact, if not anti-fact, discussion of Brexit, with its ever-escalating extremists and ineffectual moderates, provides not just scary parallels to Germany’s Weimar Republic and its doomed struggle with extremism. It also requires the EU to protect itself and its member states from any risk to its institutions and political process. Compromising its core political achievements over economic interests would be the pinnacle of political irresponsibility.

A common European future that acknowledges our fractured past and defines our collective path can only be built through a joint process, based on rules and responsibilities. Leaving the EU means leaving behind that common process and also that peace-building identity. It is not just sad, it is frightening.

• Matthias Bergmann is a German lawyer based in Hamburg