IT IS, quite simply, the European Union's greatest achievement. The offer of EU membership to its neighbours in the east and south has proved a masterly way of stabilising troubled countries and inducing them to make democratic and liberal reforms. The contrast with the United States, which despite spending billions of dollars has failed to find an equivalent policy for the countries of the Caribbean rim, is striking.

Enlargement is, however, unpopular in many older EU members. It is accused by some of making the club unwieldy. Others blame it for an unwelcome inflow of cheap labour and an outflow of jobs. Still others complain that too many countries have been let in before they were ready. Indeed, the recent wave of EU enlargement has precious few defenders in western Europe. Even fewer stand up for the principle of letting in anyone else: France is poised to confirm that any big country's membership must be put to a national referendum.

Yet scare stories about enlargement have led to false alarms. Several studies confirm that the club functions as well with 25 (now 27) members as it did with 15. Cheap labour helps hosts as well as new members. Fears of job losses and rising competition have more to do with China than eastern Europe. The economies of several old EU members, notably Germany and Austria, have gained massively from enlargement—making their hostility especially perverse. As our special report this week argues, far from joining too soon, most of eastern Europe arrived in the nick of time.

This is not to say that enlargement has been trouble-free. Some countries may have come in unprepared, notably Bulgaria and Romania. The EU mistakenly guaranteed these two, plus Cyprus, a membership date in advance, instantly losing leverage for more reforms (or, in Cyprus's case, for a deal with the north of the island). The eurocrats have learnt that, once a country is in, they have less influence on it. But less is not none. Bulgaria and Romania now face sanctions for failing to fight hard enough against corruption and organised crime.

Catching a Ukrainian wave

In any case, teething troubles with a few new members should not become an excuse for slamming the door on others. It is right for the EU to be tough in negotiating entry terms, as it is being with Croatia and Turkey, the two countries now engaged in membership talks, even if that causes delay. But to suggest that these places, or others such as the western Balkan countries, should be kept out indefinitely, regardless of their progress with reform, risks provoking instability or even downright hostility from places smack on the EU's borders.

In reality, the case for eventual EU membership of the western Balkan countries is widely understood. Turkey is more controversial, as a big and mainly Muslim country—but it is sui generis. In many ways the bigger test of the EU's commitment to enlargement lies to its east, in countries like Moldova and, above all, Ukraine. Ukraine matters: it is the largest European country after Russia, with around 46m people, a lot of fertile farmland and significant industrial capacity, including in large aircraft and steelmaking.

The recent story of Ukraine seems, at first blush, depressing. The country's political leaders have been squabbling among themselves almost since the heady “orange revolution” in the Kiev snow during the winter of 2004-05 (see article). Inflation is worryingly high and corruption is rife. Yet some encouragement can be found behind the headlines. The country's political chaos and its vigorous media are testimony to a healthy democratic debate. Although Ukraine has no oil or gas, its economy has been growing strongly. It has just joined the World Trade Organisation, ahead of Russia.

Nobody could pretend that Ukraine is ready for membership of the EU. That could take a decade or more. But it would be wrong permanently to bar it as a candidate. It is as much a part of Europe as Bulgaria, and arguably more so than Turkey. Although many Ukrainians have doubts about joining NATO, almost all—even in the Russian-speaking east of the country—want to get into the EU. If Ukraine were kept out, it could easily fall back under the sway of a newly resurgent Russia; and the knock-on effects for other vulnerable places, such as Georgia and Moldova, could be serious. If, on the contrary, it were welcomed as a candidate, that would hugely encourage liberals who hope to bring proper democracy to Russia as well. It is high time that western Europe's political leaders began explaining to their voters just why both past and future enlargement of the EU is so much in their own interests.