As the Islamic State claims responsibility for killing more than 30 people in three bomb blasts in Brussels, Europe’s debate over whether to accept the thousands of migrants trying to escape conflict just got more complicated. Many Europeans will fear terrorism – and therefore, migrant Muslims — more keenly than they will empathize with refugees who risk death to reach calmer shores.

And that exposes a deep crisis of European political identity. Deciding whom to include and whom to exclude is an exercise in defining who “we” are as a people. And that’s an ethical question about key moral principles. Which ethical path will Europe take?

In my new book, The Muslim Question in Europe: Political Controversies and Public Philosophies, I examine the political debates about whether and how European societies should incorporate Muslims. That debate reveals an ongoing struggle among three competing visions of what moral principles should guide and define the government, which I label “liberalism,” “nationalism” and “postmodernism.”

Liberalism. Liberalism started as a product and project of the European Enlightenment. Intellectual pioneers  like John Locke, Jean-Jacques Rousseau, and Immanuel Kant worked to discern and articulate universal principles that they believed showed that all people yearn to be free. Liberalism asserts the inherent equality of all persons everywhere. From this fundamental equality it derives an inviolable right of each person to think, worship, work, and live as he or she wishes so long as he or she does not impede another’s right to do the same.

What does this philosophy say about refugees? It dictates that every person fleeing grave danger or persecution deserves safe haven, for as long as the threat remains. Currently, the staunchest defender of the principle is German Chancellor Angela Merkel, who has steadfastly refused to limit the number of refugees that her country will accept. That totaled more than 1 million in 2015. Many refugees and their advocates articulate the same idea when they use slogans like “We are people not passports” or “No human is illegal.”

Merkel has her critics, including within her own party, the Christian Democratic Union (CDU). The CDU suffered historic losses in regional elections held March 13, which many attribute to the open-door policy. Merkel notes, in response, that in all three regions most voters backed parties that do support her policy.

But many people and governments in Europe oppose the open-door asylum policy. Slovakia, Poland, Hungary and the Czech Republic refuse to accept Muslim asylum-seekers. Hungary, Slovenia and Macedonia went so far as to erect barbed-wire fences to keep out refugees trying to travel through their territories from Greece. France claims it will accept only 24,000 refugees until 2017, and Britain announced it will take 20,000 until 2020.

Even previously magnanimous countries, including Austria and Sweden, have imposed limits for 2016. And on March 18, Merkel herself led the European Union to cut a deal with Turkey to receive returned asylum-seekers from Greece — reducing their number in the E.U. — in exchange for $6.6 billion and visa-free travel for Turks to Europe.

Nationalism.  Most proponents of limits invoke some form of nationalist moral reasoning.

Nationalism emerged in protest against liberal universalism. Coined by Johann Herder in 1774, “nationalism” first came into common political parlance in the middle of the 19th century. Well before that, intellectuals like Herder, Edmund Burke, Johann Fichte, Joseph de Maistre, and Giuseppe Mazzini, all of whom abhorred the French Revolution’s universalism, rejected the Enlightenment’s pivotal notion of a single, universal human nature.

Instead, they maintained that people were fundamentally different and that these inerasable differences came from their membership in different nations. Each nation was said to possess a particular character — Herder called it a “soul” (Volksgeist) — that organically takes shape from a given nation’s shared history, language and homeland, as well as common customs, mores and tastes. And these people, nationalism asserts, also share a common expectation and hope that their own nation will survive and thrive into the future so that their progeny will be able to inherit, honor and contribute to their culture and its collective achievements.

Nationalism further teaches that to thrive, each nation must maintain a certain degree of homogeneity and solidarity (“social glue”). From this perspective  the arrival of large numbers of foreigners threatens that homogeneity — especially if those new arrivals are not quickly assimilated into the dominant culture. Nationalism thus frames migrants and refugees as existential threats to national well-being: They allegedly commit crimes, take jobs, strain the welfare state and make natives feel like “foreigners in their own land.”

Postmodernism. The third ethical principle in Europe’s current migrant debate is postmodernism. Postmodernism, which arguably originated with Friedrich Nietzsche and his assault on objectivity, rejects the idea that there is such a thing as absolute truth. Postmodernism suggests that we can only know our contingent, biased perspectives, which are themselves based on incomplete information and therefore constitute lies. Driving each of our perspectives is a hidden, deep-rooted will to power, a usually unconscious psychological urge to dominate others by forcing them to conform to our preferred interpretation of how the world ought to be.

Postmodernism has seeped deep into our political culture. Its sway manifests itself in the widely held (if unacknowledged) notion that truth is whatever passes for truth (expressed cleverly by Stephen Colbert’s concept of “truthiness”), and that voters can be easily duped and manipulated with shrewdly marketed humbug.

Europe’s anti-Islam rhetoric is a perfect example of this postmodern strategy. Muslims are said to be overrunning, even “Islamicizing,” Europe, when in fact they represent just 4 percent of the E.U.’s total population. Muslims are portrayed as having a greater propensity for violence, especially terrorism, when in fact Europol reports that attacks invoking Islamic extremists typically represent less than 3 percent of failed, foiled or completed terrorist acts in a given year.

In an interview with the London Evening Standard (Feb. 2, 2007), prominent Dutch feminist Ayaan Hirsi Ali alleged that “violence is inherent in Islam. It’s a destructive, nihilistic cult of death. It legitimizes murder.” In her bestseller Londonistan, Melanie Phillips contended that “the job of subjugating the West is half done” and is being carried out by a “lethal and many-headed hydra” of al-Qaeda affiliates in Europe. Similar distortions reach millions via numerous Islamophobic websites such as Islam Watch or Stop the Islamization of Europe.

So who’s winning?

None of these three public philosophies has been able to decisively defeat its two rivals. Each has been so persuasively articulated, justified and distributed that Europeans, collectively speaking, have not been able to commit to one or another.

Many worry that the forces of exclusion are ascendant, ready to erect “Fortress Europe,” which is insensitive to human suffering beyond its borders. Surely, the attacks in Brussels this week will give a boost to such efforts. But liberalism remains very influential and won’t let Europe close its doors completely.

But neither can liberalism’s humanitarianism decisively defeat the nationalists or postmodernists. All sides will surely continue to distort and manipulate “the facts.” What Europe faces will be  contradictory policies (accepting refugees one day, excluding them the next), often based on grossly inaccurate information.