On Thursday night, President Donald Trump announced that the US had launched strikes against the regime of Syrian president Bashar al-Assad in retaliation for Assad's use of the chemical weapon sarin in an attack that killed dozens of civilians. "No child of God," Trump said in a statement, "should ever suffer such horror."

But the damage has already been done — and America, including President Trump himself, is already deeply culpable. Not because the US has shown undue hesitancy in dropping bombs on Syria before now, but because of its refusal to let Syrians help themselves by allowing more refugees to move to the United States. Expanding refugee resettlement would certainly work, would carry little in the way of short-term financial costs, and that would likely provide a powerful boost to the US economy and drastically increase the living standards of Syrians who were able to relocate. Instead, Trump has sought to slash the number of Syrians allowed to come to the US — while dropping bombs on Syria itself.

Letting Syrians come to the US would benefit them enormously, and quite possibly pay for itself

If we're actually serious about helping Syrian people — both people who've stayed and refugees — it's not enough to identify an intervention that seems like it could make things better and then declare that it's the only viable solution. You have to compare it with alternative plans, and see which produces the most good at the least cost. And it's very, very hard to argue that any military intervention that could avert further bloodshed in Syria — or even have prevented the bloodshed of the last four years — would have done more good, at lower cost, than this: simply issuing green cards to every Syrian who wants one — or even issuing them to just 1 million, or 500,000 — and providing airlifts to bring people here.

Let's take immigration to start. The potential benefits to Syrians are enormous. For one thing, we would avoid the huge humanitarian toll associated with existing refugee migration. Many fewer boats would capsize. Many fewer children would drown. Many fewer people would suffocate in the back of trucks.

The economic benefits are massive, as well. According to research from economists Michael Clemens, Claudio E. Montenegro, and Lant Pritchett, a worker born in Egypt but living in the United States makes 12 times as much as an identical worker still in Egypt. A worker born in Yemen makes more than 15 times as much as his counterpart who stayed behind. Even in Jordan, Syria's substantially richer neighbor, migrants make almost six times as much.

Finally, there's the basic fact that millions of Syrians want to leave Syria. They're willing to risk their lives to make it to a rich Western country.

President Donald Trump knows this. It's why he's made Syrian refugees a key issue in his first weeks in office. But instead of helping them by giving them what they want, he's made two separate attempts to prohibit them from coming to the US. In his first travel ban, signed during his first week in office, Trump singled out Syrian refugees for an indefinite ban from entering the US; in the second version of the ban, signed in March, Syrian refugees were included in an attempted 120-day pause on the entire US refugee program.

Either of these policies would have resulted in thousands of Syrians who otherwise would have been able to enter the United States no longer being allowed to do so. And while the first travel ban was abandoned and the second is tied up in court, the Trump administration's stated desire to slash the number of refugees allowed into the US during a given year — and its particular skepticism about refugees from Syria —strongly suggests that it's going to let fewer Syrians come to the US than its predecessor (who himself admitted many fewer Syrians than wanted to come).

The cost to the US is small at worst and quite possibly negative

What's the case against? President Trump claims that refugees in general and Syrians in particular are potential terrorists — but the odds that a Syrian refugee will commit a terrorist attack in the US are absurdly small, while the odds that the same person will suffer if not allowed to enter the US are extremely high.

It's true that flying people in and giving them basic resettlement support would cost money. Not a lot of money, but some. But over time, it would quite possibly pay for itself. It's uncontroversial among economists that immigration generates economic growth, and even the most immigration-skeptical economists concede that some of those gains go to native-born workers, not just migrants.

High-quality studies that use "natural experiments" — cases where there was a big, unexpected spike in immigration — suggest that the absolute effect of immigration on native workers is neutral or positive. It's much easier to isolate the effect on native workers in those cases than it is by trying to statistically weed out other potential causes of changes in wages. The Mariel boatlift, when Cuba unexpectedly sent 125,000 people to Florida, did not hurt employment or wages among native workers in Miami at all. A huge spike in Russian immigration to Israel in the early 1990s appeared to give existing workers a nearly 9 percent raise.

As economist Michael Clemens once told me, the effect of immigration on real wages for native workers is "definitely positive, without any doubt whatsoever." A recent evidence review by researcher David Roodman confirms this: While low-skilled immigration can make the existing low-skilled immigrant population worse off (though almost certainly not worse off than in their country of origin), Americans born here have very little to worry about, and a lot to gain.

We don't know if earlier intervention in Syria would've saved lives — and if so, how many

Letting in Syrian refugees looks pretty promising. The benefits to Syrians are enormous. The cost to the US is small at worst and quite possibly negative. So how would a military strike compare?

It's doubtful the approach of only-missile-strikes taken by Trump so far will do much to prevent civilian casualties. But let's look at the military option that would have averted the most bloodshed so far — the options on the table back in 2011 and 2012, when the brutality of Assad's attacks on Syrians was just becoming a matter of international concern.

The most common proposal at the time, floated by former State Department Policy Planning Director Anne-Marie Slaughter, the Center on Foreign Relations' Steven A. Cook, and the Henry Jackson Society, among others, was to use Western air power to create and defend special "no-kill zones." These would be areas close to the Turkish, Lebanese, and Jordanian borders that would receive humanitarian aid and provide a base from which to train and arm opposition groups. Benghazi served a similar role in Libya; after being defended by NATO air power, it provided a base in which opposition groups could start building a government in exile and plan operations against the Gadhafi regime.

I genuinely don't know if that would've worked. But there's a lot of reason for doubt, and plenty of reason to think that creating such zones would be extremely costly.

For one thing, the political science literature on arms support to rebel groups suggests that, more often than not, they drag out conflicts rather than bringing them to a swifter end. George Washington University professor Marc Lynch notes that the particular characteristics of the Syria conflict — where the goals of the West and those of the rebels aren't identical, where the rebels are fractured, where the foreign countries intervening aren't all on the same side — made it a particularly unpromising conflict in which to take that approach.

Lynch also points out that, in practice, supporting a "no-kill zone" would require much more than airstrikes. If it were unprotected and the Syrian military were allowed to attack within it, you'd have a repeat of the Srebrenica debacle, in which Serbian forces were able to massacre Bosnians within a UN-declared "safe area" because the UN troop deployment was insufficient to stop them. But defending such an area successfully would require a significant investment of troops.

"If Srebrenica is the worst-case, the experience of the relatively successful Operation Provide Comfort in northern Iraq after 1991 should prove equally sobering," Lynch writes. "An operation which was envisioned as a short term response to crisis, on the expectation of Saddam Hussein’s imminent fall, instead turned into a decade-long commitment. Maintaining that safe area required some 20,000 troops, near-constant air-raids, and an increasingly contentious international debate at the UN which consumed the Clinton Administration’s international diplomacy."

Mere airstrikes wouldn't have been enough to stop the killing, in other words. For one thing, many of the civilian casualties being endured at the time were occurring due to the Assad regime's assaults on contested cities. The US could not have bombed Assad's forces in those cities without running the risk of killing more civilians than it saved.

Ultimately, the choice was whether to commit tens of billions of dollars, and tens of thousands of US ground troops, to implement a strategy that might have toppled Assad and saved thousands of lives, but which also might have made the conflict even more brutal than it's been. The latter was probably more likely, in fact. The cost would have been considerable in any case, and the benefit very uncertain. Compared with the benefits of letting Syrian refugees into the US, which we know are great, and the costs, which we know are small, that's not a very attractive proposition.

The best humanitarian interventions don't involve the military

American elite enthusiasm for humanitarian airstrikes to protect civilians from civil war or genocide is peculiar. On the one hand, it's a welcome expression of empathy for the rights and welfare of people outside the United States. Strengthening cosmopolitan sentiment is a good thing indeed.

But it also enables a strange hypocrisy. The humanitarian interventionists who cheer our strike on Assad, and who urge further action to push him out of Syria entirely, aren't spending the rest of their time arguing that we should boost funding for the US's hugely effective anti-HIV/AIDS program. They're not pushing the US to greatly increase its foreign aid budget in general, perhaps to 1 percent of gross national income, like Sweden, from merely 0.2 percent.

They're not calling for reforms that make it easier for USAID and other aid agencies to spend on highly effective projects that reduce child and maternal mortality. They're not calling on the US to eliminate all quotas and tariffs on goods from poor countries, as well as farm subsidies that make it harder for poor farmers in sub-Saharan Africa to export their goods. They're certainly not calling for a massive expansion in levels of immigration to the US from Haiti, the Central African Republic, the Democratic Republic of the Congo, and the rest of the world's absolute poorest countries.

Perhaps they support all those policies, and if so, good for them. But if we're serious about changing US policy so as to help as many poor, vulnerable people as we can, military strikes wind up being a tiny part of the overall picture. The real struggles are less sexy. They don't let you posture like you're tough and hardheaded. And they require fighting against interest groups that wield real power in the US.

Basically no one in Washington likes the Assad regime, so it's extremely easy to saber-rattle and make grand pronouncements about the need to crush it. But plenty of people in Washington love farm subsidies. Plenty of people in Washington like restricting immigration, especially low-skilled immigration from poor countries. Plenty of people in Washington like the idea of cutting the foreign aid budget, or perhaps eliminating it altogether. Those fights are actually hard. And they actually matter.

And right now, in 2017, no one could seriously argue that sending US ground troops has a realistic chance of ending the war and leading to a peaceful, democratic Syria. It's too late. But it's not too late to help refugees. The boats are still sailing, and sinking. Children are still dying. People are still suffering. It's not too late for the US to heed the International Rescue Committee's call for us to resettle 65,000 refugees, not the paltry 1,434 we've resettled so far. It's not too late to do the International Rescue Committee one better and let in 200,000, 500,000, 1 million even. It's not too late to make Syrian refugees' lives dramatically better.

If the loudest Syria hawks on Capitol Hill — your John McCains and Lindsey Grahams — are serious about helping Syrian civilians, they'd be pushing for President Trump to stop trying to ban refugees and to commit to filling the 33,000 spots reserved for refugees from the Near East and South Asia this fiscal year. They'd be pushing him to increase that cap, or perhaps even lift it entirely. They'd be trying to make life better for Syrians in the most effective manner available. McCain and Graham have paid lip service to the plight of refugees, and Graham has suggested he might support legislation to let more enter. But they've spent far more of their time and energy urging intervention, and admonishing the Obama administration when it wasn't forthcoming.

Morality in foreign policy isn't about bombing bad guys. It's about helping people. And usually, the best way to do that won't involve bombings at all.