Sunday 4 March will be a turning point for Europe. On the same day as an important general election in Italy we’ll find out whether an internal referendum of German Social Democrat party members has produced a yes for the grand coalition government in Berlin, continuing its current partnership with Angela Merkel’s Christian Democrats.

Conventional wisdom says this would be a good result for Europe. I think the conventional wisdom is wrong. Like putting on a medical corset to alleviate a serious back condition then carrying on with your life just as before, a grand coalition would be good in the short term but bad in the long. You need to address the causes, not just the symptoms. And there is an alternative.

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I spent two days in Berlin this week, and I’ve never encountered less enthusiasm for a prospective new government. This is supposed to be a wedding, but it feels like a funeral. That is also what it could prove to be: the funeral of the SPD, one of Europe’s oldest and most important parties of the centre left. In a shocking public opinion poll a few days ago, the far-right, nationalist-populist Alternative for Germany (AfD) scored 16%, half a point ahead of the Social Democrats. That may be a flash in the pan, but at 20.5%, the Social Democrats’ result in the last general election was already an all-time low.

We know from history that a grand coalition of the main centre-left and main centre-right parties tends to strengthen the extremes – and this has already happened. It was partly as a result of there having been this same grand coalition – or GroKo (for Grosse Koalition) – for eight of the previous 12 years that the AfD garnered the support of one in eight German voters in last September’s election. And remember that the AfD makes Ukip look moderate, and Silvio Berlusconi seem like a distinguished conservative gentleman.

A crucial part of the response to the wave of anti-liberal populism flooding across Europe must be a fundamental regeneration of the centre left. The French Socialists have virtually disappeared from view, and in the Italian election campaign Matteo Renzi’s Democratic party is doing almost as badly as the SPD. It is clearly impossible for the German Social Democrats to regenerate their party while locked in a joyless governing coalition with their main opponents. That is one reason why the Young Socialists, led by a man called Kevin Kühnert (named after the former English football star Kevin Keegan), are touring the country trying to persuade their older comrades to vote #NoGroKo.

Conventional wisdom says that after five months, Europe badly needs a stable German government, and that government needs to give a positive response to Emmanuel Macron’s ambitious European proposals. After all, the year leading up to the 2019 European elections is meant to be a crucial one to put wind in the sails of a post-Brexit European Union. This is why European council president Donald Tusk tweeted: “German GroKo is good news.”

The worst argument of all for a grand coalition is that there is no alternative

I am not persuaded that you need a German GroKo in order to have the essential European coalitions of the willing, or that a GroKo would be better for the European project in the longer term. Play out a mildly pessimistic but entirely plausible scenario. The German economy falters in a couple of years, and at the same time eurozone arrangements put in place by the grand coalition – responding to Macron at the insistence of the Social Democrats – result in Germany having to make financial transfers to a crisis-torn southern European state. Imagine the response among disgruntled German voters. Twenty per cent for the AfD?

The worst argument of all for a grand coalition is the one produced as a clincher in my Berlin conversations: there is no alternative. But the elite politics of Merkel’s now famous alternativlos, a new version of Margaret Thatcher’s Tina (There Is No Alternative), is precisely what voters are rebelling against when they choose the AfD, or Donald Trump, or Brexit. Imagine that you’re an unhappy German voter. You voted last September to change something. Then absolutely nothing changes: same chancellor, same coalition, same woolly rhetoric, very similar policies.

To be sure, new elections now, after five months of unprecedented political muddle, might produce an even larger protest vote for the AfD. But there is a better alternative, which the chancellor and federal president could agree to try if the Social Democrat party membership votes no: a Merkel-led Christian Democrat minority government. Minority government would be an innovation in the history of the Federal Republic. But it has been done in many other democracies, and there’s nothing in the German constitution that says you can’t do it. Indeed, the very strong position that constitution deliberately gives to the chancellor might make it easier to sustain a minority government. The mainstream opposition parties, Free Democrats and Greens as well as Social Democrats, would surely offer support on the main, consensual thrust of European or security policy, as well as budget and confidence votes. Yes, the minority government would lose some parliamentary votes on other issues, but as the German historian Heinrich-August Winkler points out, that would actually increase the importance of parliamentary debates and the work of select committees. Would that be bad for a parliamentary democracy? Quite the reverse.

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Berlin’s response to Macron’s European proposals would be somewhat less enthusiastic, especially in relation to the eurozone. But that would be a realistic reflection of where most Germans are on this, which is a very long way from former SPD leader Martin Schulz’s vision of a United States of Europe by 2025. At the same time, the Christian Democrats might feel impelled to offer Macron more on a common foreign, security and defence policy – especially when faced with the terrible trio of Brexit, Trump and Putin. Would that be bad for Europe? Quite the reverse.

A minority government under Merkel probably would not last a full term, but that would also not be end of the world. I’m a great admirer of Merkel, but we are definitely approaching the time for a change at the top. That, too, is democracy. An election in 2019 or 2020 with sharper opposition parties, and with a new, younger leader of the Christian Democrats, would hardly be worse than one forced on a stale and crumbling grand coalition.

The motto silently hanging over the conventional wisdom of Berlin is a conservative one first used in 1957: Keine Experimente! (No experiments). But what Germany needs now is rather Willy Brandt’s cry from 1969, Mehr Demokratie wagen! (Risk more democracy!). The experiment of a minority government would create some uncertainties in the short term, but in the long run it would be better for Germany and for Europe.

• Timothy Garton Ash is a Guardian columnist