If Jean-Claude Juncker gets the job as European commission president this week, which now looks almost certain, it will make a mockery of European democracy. The fact that David Cameron and the Tory backbenches recognise it doesn't make it any less true.

Instinctively the left is practised at leaping to the defence of Europe against a constant barrage of rightwing hostility. It's almost automatic – the right despises the European project, therefore there must be something in it, so the logic goes. And broadly speaking I would agree. On most of today's big issues the era of the nation state is over. On everything from taxation to climate change, meaningful reform increasingly comes through concerted transnational action rather than unilateralism – especially for a small country like Britain.

Unthinkingly leaping to the defence of European in its current form, however, would be a mistake. And acquiescing in the ascendance of Juncker simply because Cameron dislikes him would be worse: it would play up to every anti-EU stereotype of rightwing caricature.

It's not only that Juncker is a typical establishment bureaucrat, although that does matter; it's that his election will be a further step for Europe down a profoundly undemocratic road. Juncker's claim to the top job, which he arrogantly believes will be his as long as "common sense prevails", is about as flimsy as a plastic bag.

As the leader of the European People's party, the largest bloc in the European parliament, Juncker believes he has an electoral mandate to assume the presidency based on the recent European elections. Yet who went to the polls last month with a view to voting for the next president of the European commission? Who cast their vote with a middling bureaucrat from Luxembourg in mind? Indeed, in a recent survey, only one in 10 European voters even knew who he was. So much for a "popular mandate".

And then there is Juncker himself, a man whose only political achievement has been to win power and keep it in not so much a country as a bolthole for the sort of person who views the payment of tax as optional. On his watch, Luxembourg assumed and held on to notoriety as the EU's top tax haven; or in the politically correct language of the country's finance minister, it became an esteemed "centre of finance".

Eurosceptics are still wrong when they conclude from all of this that the entire European project must be trashed. This is the childish and philistine option; it is always easier, after all, to chop down a tree than to prune it effectively. Eurosceptics should also be watching the resurgence of autocratic Russia with embarrassment: Vladimir Putin is the most passionate anti-EU politician for a reason.

But the left should be kicking off about the rise of Juncker, not leaving it to Cameron. The disturbing growth of the far-right demonstrates that now is not the time for business-as-usual in a Europe that most people view as bureaucratic and distant. Business as usual is exactly what Juncker represents.

To call yourself a democrat, your attachment to the principle of democracy must be stronger than your attachment to any specific political doctrine, including that of European integration. You can't be half a gangster, said a character in the drama series Boardwalk Empire, and you can't be half a democrat either.

Cameron has certainly "fucked up", as the Polish foreign minister phrased it, in his battle to prevent Juncker from assuming the top job. But the left has also "fucked up" in not lamenting more loudly the gaping hole in Europe's democracy.