ROME—Fifty years ago in this city, six countries signed the Treaty of Rome and gave birth to what we know today as the European Union. As a European citizen, I am torn between what I like and what I don’t like about this creature. In this, I am no different than most Europeans. Janus, the two-faced Roman god of transition who looked backward and forward at the same time, is the image that comes to mind on this half-century anniversary.

What is best about the European Union comes from the countries that were not part of the founding club. It includes the cultural leap from provincialism to globalization (Spain, Ireland, Portugal), the transition from communism to liberal democracy under the rule of law (the countries that joined in 2004), and that measure of British skepticism which has diminished somewhat the constructivist, top-down dimension of the union.

What is worst about the European Union comes from the founding countries, particularly France, Germany and Italy. Although some timid reforms have taken place in Germany and Italians remain creative and productive despite their labyrinthine politics and regulations, the founding club is responsible for the economic sloth that has turned so many young Europeans against their institutions. The damage caused by these countries’ protectionist laws and bankrupt welfare systems is compounded by the fact that most of the victims, especially the unemployed, blame their fate on free enterprise—precisely what has been missing in many areas, from labor regulations to agricultural policy.

Others blame immigration. However, the evidence indicates that immigration has been largely beneficial. In fact, some of the countries that have been doing best in recent times—Ireland, Britain, Sweden—are ones that allowed the newcomers to the union to work within their borders almost from the start. Also, countries such as Spain where fertility rates had plummeted are beginning to reverse that trend precisely because of immigration. The irony of this is that immigrants, who are blamed for plundering the welfare state, are actually prolonging its inept existence because they have reduced the gap between those who contribute and those who benefit.

As I landed in Rome, I was rereading Joseph Conrad’s “The Secret Agent.” I came across a famous passage in which a foreign diplomat, perhaps Russian, instructs the British agent to plant a bomb in London in order to shock the Brits into being less respectful of established rights and legal procedures at a time—the 1890s—when anarchist terrorism was making it necessary, in his view, to reinforce autocracy. “This country is absurd with its sentimental regard for individual liberty,” Mr. Vladimir tells Mr. Verloc, the agent.

One can easily picture Russian President Vladimir Putin saying something like this to one of his counterparts in the European Union today. However, when one hears European leaders praise the achievements of the union over the last 50 years—namely, peace and prosperity—one gets the impression that they attribute the absence of wars among the member states and the wealth that they broadly enjoy to the top-down, bureaucratic part of European integration. The real reason for that peace and prosperity has to do with that “sentimental regard for individual liberty” which has continued to govern European societies despite the centralized and bureaucratic aspects of integration. To that principle we owe what we can characterize—despite some subsisting restrictions that will eventually wither away—as the free flow of people, goods, capital, services and ideas among the 27 member nations.

To that same principle we owe, too, the formidable battle that the more enlightened members of the union, particularly Central and Eastern Europeans, are waging against those who favor a “fortress Europe”—protectionist, anti-American, and heavily centralized—and those who, like French Gaullists, harbor nationalist illusions of grandeur.

In today’s world, the only way to ensure that the European Union continues to be prosperous and peaceful is to make it as open, flexible and decentralized as possible. This will mean being less anxious about forcing a European identity into the imagination of dissatisfied European citizens by conjuring up grandiose schemes, and being more concerned with removing the barriers that make so many youngsters unable to exercise the expanded choices that globalization has to offer.

Eventually, Janus, the god of doorways, will have to decide whether to go in or get out. The job, in the next 50 years, is to push him in and close the door behind forever.