Countries like Qatar and Saudi Arabia are basically accepting no refugees. The U.S. is accepting relatively few. And the countries that have opened the door widest are places like Germany and Sweden, which are motivated by a different theory of moral obligation: A utilitarian universalism, which holds that the world’s wealthy nations have an obligation to accept refugees, period, regardless of whether their own governments bear any responsibility for the crisis that produced them.

This theory has the advantage of eliminating any messy haggling over who bears responsibility for what. When tragedy strikes, everybody above a certain level of G.D.P. just has to open the gates. (Or, perhaps, to have them open permanently.)

But it has the disadvantage of being completely unworkable over the long run, as Europe is beginning to discover. The utilitarian theory is blind to the realities of culture, the challenges of assimilation, the dangers and inevitability of backlash. It takes what is a deep, long-term issue for European society — one way or another, over the next century the continent will have to absorb large numbers of new arrivals, from Africa especially — and brings things to a crisis point right now. And then it tries to evade that crisis by treating dissent as illegitimate, which only works until it doesn’t: One day you have a pro-immigration “consensus,” and the next a party with fascist roots is leading Sweden’s polls.