Donald Tusk: afraid of revolution. AP Photo/Alik Keplicz A spectre is haunting Europe — the spectre of Grexit.

And, as Marx would have noted with a smile if he were still alive, Europe's leaders are now, unusually, openly worrying about whether the high cost of the Greece bailout might lead to "violence" or "revolution."

German Chancellor Angela Merkel on Friday urged the Bundestag to pass the bailout and keep Greece in, using these words, the Financial Times said:

She emphatically rejected the alternatives of stretching further the EU laws until they lost their meaning, and a sudden Grexit which could bring "chaos and violence" to Greece.

Late Thursday night, European Council leader Donald Tusk told the FT:

"I am really afraid of this ideological or political contagion, not financial contagion, of this Greek crisis," said Mr Tusk.

... "For me, the atmosphere is a little similar to the time after 1968 in Europe," he said.

"I can feel, maybe not a revolutionary mood, but something like widespread impatience. When impatience becomes not an individual but a social experience of feeling, this is the introduction for revolutions."

That is extraordinary.

Greek protesters rioting in front of the parliament building in Athens this week. REUTERS/Jean-Paul Pelissier It was one thing when the Greeks, internally, began wondering aloud whether the fight over staying in the European Union would lead to a second Greek civil war. The Greeks have always had a strong leftist side to their internal politics, a flank Britain and Germany discarded 15 or 20 years ago.

But now politicians are starting to worry that the anti-EU threat comes not from the right — where nationalist parties such as the UK's UKIP get their votes — but from the left.

If Greece goes wrong — it can still default on its new debts, which International Monetary Fund chief Christine Lagarde on Friday said was "categorically" not viable — then the equivalents of Greece's left-wing Syriza party are waiting elsewhere in Europe: Podemos in Spain and the Five Star Movement in Italy. Why shouldn't they stage their own revolutions against the EU? It sure sounds better than following the Greek path.

Viewed from either side of the political spectrum, the EU looks like a disaster right now:

The conservatives are proved correct about the way the EU takes away national sovereignty: The Greeks voted in a referendum to reject the bailout ... but were forced to accept it anyway.

The Greeks voted in a referendum to reject the bailout ... but were forced to accept it anyway. And the leftists are proved correct about the way the banks control everything and everyone else gets screwed: The Greek economy has been brought to its knees by debt, provided first by private investment banks such as Goldman Sachs and then by Europe's ruling German-French elite in the IMF and the EU. The entire bailout is structured to benefit the lending banks the most, not the people of Greece.

Suddenly the tinfoil-hat conspiracy theorists look as if they were right all along!

This is the environment into which British Prime Minister David Cameron is calling for a national in/out referendum on the EU in the UK next year.

He couldn't have picked a worse time.