Instead of celebrating the admission of 10 new members (eight of them former communist states), the west's political elite has buckled under populist campaigns directed against "Polish plumbers" and alleged Roma benefit scroungers.
"Before, the rockets of the east were pointed at us - that was scary," remarked Jean-Claude Juncker, the sardonic Luxembourg prime minister. "Today the hopes of people from central and eastern Europe are pointed at us - and surprisingly that is even scarier than rockets."
The EU's enlargement from 15 to 25 member states in 2004 brought the forces of globalisation within the walls of the western club, heightening public fears of job losses and "delocalisation" of factories to the low-cost east.
Unable to explain the economic benefits or the historical context of this momentous event, politicians respon-ded by putting up barriers. Citizens from Bulgaria and Romania - the next countries to join the EU in 2007 - will face work restrictions. Meanwhile, membership hopes in the Balkans, Turkey and Ukraine have been thrown into doubt.
Olli Rehn, the EU's enlargement commissioner, has written a no-nonsense tract dismantling the arguments of those who want to halt the process now and to define strictly the future "borders" of Europe, preferably to the west of the Bosphorus.
"There is something rotten in the Union of Europe today: our utterly defensive attitude to change," the Finn writes. Rather than talk about fixing borders, Mr Rehn wants Europeans to view the lands to the east as exciting frontiers to be tackled and tamed.
He also urges Europe's leaders to raise their eyes. His is a vast EU of 35 or more members with a population of 600m or more, with the economic muscle to strike favourable trade deals and impose standardson the world.
Mr Rehn approvingly cites Eric Hobsbawm, the Marxist historian: "Geographically, as everyone knows, Europe has no eastern borders and the continent therefore exists exclusively as an intellectual construct."
Since the Union is open to any country that complies with the club's values and that is "European", the membership criteria are either worryingly or fortuitously vague.
Mr Rehn likes it that way, since he believes the prospect, however distant, of EU membership helps countries carry out the painful legal, political and judicial reforms that are the Union's minimum requirements.
Morocco's bid to join was rejected because the map locates it firmly in Africa. But if Turkey's membership aspirations have been recognised, how can the EU turn its back on the former Soviet republics of Ukraine, Belarus, Moldova, Georgia and Armenia?
Mr Rehn takes on criticisms of this maximalist strategy one by one. He cites economic studies showing that the recent "big bang" enlargement into central Europe has benefited "old" and "new" members alike. Migrant workers have filled gaps in the labour market in the west and prosperity has increased.
He says the costs have been manageable too. "One or two cups of coffee per month is the price each citizen of the 'old' member states has paid to help reunite Europe," he claims. Fast-growing new members also buy most of their imports from western Europe, so aid going out comes back in the form of orders for BMWs.
What about the argument from federalists that the expansion of the EU weakens its ability to act, turning it into little more than a free trade area?
Mr Rehn concedes there are teething problems associated with running a club of 25, but argues: "In the course of the history of the EU, deepening and widening have moved together in parallel, sometimes even hand-in-hand."
He explains that the original Europe of Six did not even complete the single market. That only came after 1986, when the club had reached 12. The common foreign policy and the euro came as the club moved towards 15 members; the constitution, now in cold storage, was agreed after it reached 25.
Mr Rehn's views matter. Although national capitals take final decisions on Europe's future shape, he is charged with keeping fraught membership negotiations on track.
It is an uphill struggle and Europe's Next Frontiers is light on details of how selling enlargement has been made even harder through past blunders, including agreeing to let Bulgaria and Romania join when they were not fully ready. Brussels also badly underestimated the likely scale of westward migration after the 2004 expansion.
Mr Rehn is more concerned about the future, filling in the "black hole" in the EU's map where the former Yugoslavia used to be, making Turkey "an even sturdier bridge between civilisations" and keeping the door open for others. Some elected politicians quake at the prospect. But Mr Rehn, a Brussels functionary, does not have to worry about elections: "It's a tall order, but it is also a beautiful mission."