Morality is a tricky thing.

Pretty much everyone presumes that morality is a good thing. But few face up to just how multifaceted and even downright contradictory it can be, pulling us in different directions, making conflicting demands. We all know that it's just plain wrong to lie, for example. And yet we also know that in some situations — when Nazis show up at your door in search of the family of Jews you're hiding in your basement — it can actually be morally wrong to tell the truth.

One response to the changeable character of right and wrong — the smart response — is to recognize the need for prudence, for practical wisdom to weigh various contrary considerations and decide when it's necessary to make trade-offs among them.

And then there's the other response — one that can be seen whenever someone confronts the complications and complexities of moral demands by denying the need for trade-offs, because (they foolishly insist) one whole aspect of moral phenomena can be dismissed. This makes moral deliberation vastly easier, but at the cost of distorting our moral experience, which becomes abundantly clear once decisions are made on the basis of the distorted view, producing patently irresponsible behavior.

The folly of the second, simplifying response to moral complexity has been obvious this week on both sides of the debate about whether, in the wake of ISIS's terrorist attack in Paris, the United States should go forward with President Obama's plan to admit roughly 10,000 Syrian refugees into the country.

On one side are those — overwhelmingly, but not exclusively, Republicans — who oppose admitting any refugees. Though they don't use the language explicitly, their (majority) position is based on a concern for the common good of the United States, which includes protecting the political community from the harm that would be inflicted if one or more of the refugees resorted to terrorism after settling in the country.

This is a legitimate concern, though in this case it is probably misplaced. The United States is a very large country with a population of 318 million people. We're talking about taking in just a few thousand refugees, many of them children, and subjecting the adults to a form of background screening that has proven to be remarkably effective. As many have pointed out, the U.S. has allowed roughly 800,000 refugees to settle in the country since 2001 — and not one of them has resorted to terrorism. The likelihood that, once admitted, one of this latest batch of refugees will either turn out to be a covert ISIS operative or become a jihadist after arriving here, is quite small.

And then there are the competing moral considerations.

In addition to defending the common good, morality calls on us to give each person what he or she is owed or deserves. One way of determining what a person deserves is to follow the rule of law.

But the United States is a nation devoted to higher principles than human-authored law. Most of us believe (at least sometimes) that our laws derive from or appeal to a moral law that applies to all human beings, not just to U.S. citizens. Some conceive of this higher law in terms of inalienable human rights grounded in the American founders' deistic "nature and nature's God." Others fall back on more traditionally Judeo-Christian notions of loving God and one's neighbor (defined very broadly to mean all creatures made in the image of the deity). Still others appeal to a secular ideal of universal humanitarianism.

Whatever its source, a powerful stream of American moral conviction dictates that, in certain circumstances at least, those from outside the political community deserve to be treated as equals. When, for example, a Syrian family fleeing from years of unspeakable violence and turmoil shows up on our proverbial doorstep begging for assistance, our moral ideals demand that we let them in.

In coming down so strongly against admitting any refugees — in giving consideration only to the demands of the common good and not at all to what we owe to suffering human beings in flight from the chaos and bloodshed in Syria — the Republican candidates for president and more than half of the nation's governors are acting in an un-American (and un-Christian) way.

But they aren't the only ones who deserve some blame in this debate. Too many of those on the opposite side — many Democrats and some Christian organizations — make the same mistake, but in reverse.

Uniformly focused on what they believe we owe to the Syria refugees, many Americans who favor opening our doors to those fleeing the war zone seem indifferent to concerns about the common good. Going far beyond prudentially denying that the refugees pose a significant threat, many imply with their curt and angry dismissals of those on the other side of the issue that they must be motivated by moral indifference, selfishness, cowardice, and even baser motives, like racism. We've also heard a fair amount of sophistry about how closing our borders to refugees would be tantamount to siding with ISIS.

It's almost as if some on the pro-refugee side of the argument consider it illegitimate to take into account threats to the common good when formulating our country's policies on this subject.

If some on this side of the Atlantic (including the president of the United States) have edged in that direction over the past week, many more do so regularly in Europe, since the entire EU project is premised on the view that the common good of particularistic, national entities lacks the moral standing of universalistic humanitarian ideals. The result has been wildly one-sided policymaking, with Germany and France favoring the admission of hundreds of thousands of refugees with very little if any consideration of consequences, now or in the future.

This would be bad enough if it merely meant that the continent would face the threat of jihadists entering the EU along with those genuinely fleeing the Syrian war zone. But the graver danger lies in the future. Europeans do many things well, but assimilating Arab-Muslim immigrants is not one of them. As Adam Garfinkle recently put it in an essential essay in The American Interest about Europe's refugee crisis, "if only a tenth of one percent of these Arabs are now or are later turned toward salafi-based political violence," then the continent will face a crisis that makes the murderous mayhem of last weekend seem like child's play.

And all because politicians and policymakers followed one part of morality to the exclusion of another.

As the great literary critic Lionel Trilling liked to point out, exercising moral intelligence is exigent, strenuous business, requiring us to weigh conflicting irreducible goods against each other and sometimes to choose in favor of one and against the other. The necessary trade-offs can be agonized over and lamented, but they can't be wished away and should never be denied.

Too many of our public leaders are making a pernicious and unimpressive habit of going easy on themselves.