Pro-Europeans will, for the most part, fight the EU referendum on pragmatism, ideas of Britain and the risks of leaving, and for good reason: these matter far more to most voters than the abstract idea of Europe. Most British people see the EU as a question of pros and cons. Plenty of people will make those arguments. But on Europe, I am an unashamed idealist. I believe in the European idea; I believe in the EU’s moral purpose.

Why so? For all its many faults, the EU has done more than any other organisation in history not only to help countries to co-operate, but to change the very way they relate to each other – to create a government of laws and not of men between countries and not just within them. ‘Classical’ international relations are ultimately based on power; on might making right; on the short-term and long-term calculus of interests between states, with all the insecurity and destruction that often entails. In the EU, we have rules, laws, votes and courts.

Once upon a time, Belgium was the cockpit of western Europe. It was handed from Spanish kings to Austrian Emperors; studded with Dutch-garrisoned and British-funded forts; fought over, traversed, occupied; handed to the Netherlands; given neutrality and independence; and then invaded twice in the last century, devastated twice. Now it can take its turn in the Presidency of the EU, jointly shape rules which govern much of the continent and host a directly-elected parliament representing the countries which once tore it apart.

We don’t just know we’d be mad to fight each other or conclude we have no interest in doing so: we don’t think about each other in that way anymore. Even countries like Norway and Switzerland are really debating how much they wish to integrate with the EU and how much having a direct say matters to them, not whether to be in the EU system at all. NATO and the nuclear balance may have made war impractical; the EU made it unthinkable.

The EU has promoted the rule of law within states, not just between them. We take democratic Greece, Spain, Portugal and eastern Europe for granted: but in fact, it’s astounding how far constitutional, liberal norms have been entrenched across those countries. Despite the (very real) concerns in Poland and Hungary, the creation of a swathe of liberal democracies in such a short period of time is not typical, and the European idea played a huge role in making it happen. Because countries wanted to join, they had to meet EU standards for democracies, not just markets – and not just elections, but courts, civil society and the civil service too. Britain played a major role here: as Margaret Thatcher said in her Bruges Speech, ‘We shall always look on Warsaw, Prague and Budapest as great European cities.’

If you doubt whether EU enlargement matters, look at what happens when the EU cannot deliver on its promises. When Recep Tayyip Erdoğan first took office, his government abolished the death penalty and started to improve conditions for the Kurds; Kurdish parliamentarians were released from prison, the State Security Courts were abolished and more besides. This went hand in hand with the opening of accession negotiations in 2005. As we all know, the negotiations slowed down, ground to a halt and mostly froze. The shift back to more authoritarian governance has gone hand in hand with drifting away from Europe. Macedonia had brought itself to the point where the Commission recommended accession talks; the name dispute froze the process, and we now find ourselves with a country which cannot hold credible elections in April. The EU’s not the only factor, but the contrast between countries where the EU can deliver and those where it cannot tells a powerful story.

It’s overwhelmingly in our interests to support the EU and thus a more democratic, stable, peaceful continent. Britain never could afford to stand aloof from the rest of Europe when the chips were down. But this isn’t just about that: it’s about the kind of country we want to be. I don’t want us to be the kind of country which turns its back on friends and allies; I don’t want us to define ourselves by our isolation; I want us to pride ourselves on the contribution we make to our continent and our world, not just what we get from them. Britain has, for better and for worse, almost always been engaged in the world. We now have the second-largest development budget, a seat on the Security Council, membership of the G7 – and a key place in the European Union.

We have been awkward partners in Europe, yes, but we have contributed a great deal to it too – a key role in promoting the single market, championing enlargement, co-operating on security and defence. We cannot run Europe alone: no one country can and no one country should. But we can play our part: our voice usually is heard. Germany, the Nordic countries, the Baltics and the eastern European states fear our exit precisely because we do have a voice in Europe, with which they often agree, and without which Europe would be the poorer.

It is too easy – far too easy – to be complacent about the relatively peaceful continent we now have. 70 years of peace in liberal-democratic, welfare-capitalist Europe have made it all but impossible for us to imagine the veneer of civilisation cracking again. But civilised, developed, democratic peoples descended to the depths before, and it could always happen again someday. The EU is a tool to keep states civilised in Europe; to make co-operation the norm rather than conflict; to produce fudged compromises rather than pitched battles; to try, as best we can, to work together on the basis of rules and not of might.

The EU is only one institution welding the Euro-Atlantic world together, along with NATO, the Council of Europe and others: no one is saying the end of the EU means an immediate descent into barbarism. Perhaps we’d all cope if it fell apart. But if Europe reverted to an unmitigated patchwork of squabbling states, if its ineffectuality sapped America’s will to guarantee its security, if Putin’s Russia fomented instability on democratic Europe’s border, what kind of Europe might we end up with? War in our lifetimes: almost certainly not. War in our children’s lifetimes: probably not. But war in our grandchildren’s lifetimes? This Europe can fail too: all other attempts to keep the peace in Europe have collapsed so far.

The European Union embodies a fine and precious ideal. It has changed the way Europeans deal with each other and helped spread democracy across Europe; it is a project to which Britain has given and from which we have gained a great deal. And like any fine ideal, it could collapse and fail. The EU is at risk already. It would be a tragedy, and a betrayal of our own best instincts, if Britain dealt one of the blows which tore it apart.