Syrian Refugees and the Precautionary Principle

In environmental policy, the precautionary principle states that a new product, method, or proposal whose effects are disputed or unknown should not be introduced if it is harmful. The burden of proving that it is harmless falls on its backers—virtually guaranteeing that it won’t be produced. In contrast, a cost-benefit analysis that compares the probability of harm with the expected magnitude of the benefits is a better method. 

The methods of the precautionary principle are implicitly applied by many opposing the resettlement of Syrian refugees because they deem any risk of terrorism as too great. The precautionary principle is as improper a standard for determining refugee policy as it is for guiding environmental policy. 

Arguments derived from the precautionary principles are often emotionally driven. Senator Shelby (R-AL) made such an appeal when he stated, “We don’t know much about these people. They haven’t really been vetted. They come from an area where there’s a lot of turmoil, a lot of terrorists come from. We don’t need one more terrorist; we got enough right now.”

Senator Shelby is correct that we don’t need another terrorist, but he didn’t explain that the risk of a terrorist coming through the refugee system is low. 

3,252,493 refugees were admitted to the United States from 1975-2015. During that time period, 20 of those individuals attempted to carry out a terrorist attack or succeeded in doing so inside of the United States. That is a single terrorist for every 162,625 refugees admitted or one every two years since 1975. 

Although there were only 20 refugee terrorists admitted since 1975, they have only succeeded in murdering three Americans. Each one of those murders is a tragedy but the chance that an American would be successfully killed by a refugee terrorist was one in 3.6 billion a year. Each year an American had a 0.000000028 percent chance of being murdered by a refugee terrorist each year (for those with poor eyesight, that’s seven zeros to the right of the decimal point). That’s a small risk.

But, as the implicit proponents of the precautionary principle claim, the costs of refugees in the future could be greater. Letting them in today could set up a whole raft of unforeseeable future problems unlike those of the past. That is possible. So even if the annual rate of murder from future refugee terrorist attacks is 100 times greater than it was during the 1975-2015 period, the chance of an American being murdered each year would rise to one in 36.4 million annually.

Anything could change in the future. The precautionary principle always rigs the outcome in favor of immigration restriction because it’s impossible to prove that all refugees will be harmless just like it is impossible to prove that any other person will be harmless. If the precautionary principle becomes a starting point for debate, those favoring refugees will always fail. No debate should be stacked this way.        

Perhaps the victims of terrorism from refugees should be very heavily weighted than other deaths in any risk calculation. Perhaps the threat from ISIS or Syrian refugees is unlike any ever faced and more caution is warranted (highly, highly unlikely). Perhaps our social, political, economic institutions are more fragile than they appear and could be easily undone by a few refugee terrorists. Any of those factors being true could tilt the cost-benefits scales against admitting Syrian refugees, but such dire predictions are currently unwarranted and must be weighed against the costs of not admitting Syrian refugees. 

Unforeseen Costs of Barring Refugees

There are costs to current Americans for not granting entry to some Syrian refugees. Barring their admission could create a greater security risk in the future. Refugees who languish in refugee camps for years or decades are more likely to be radicalized and become terrorists. Under such a situation, allowing them to resettle in the United States could drain the swamp and decrease the fecundity of terrorist breeding grounds.

Refugees going to other countries, like Sweden, often settle in horrid welfare-subsidized situations in over-regulated labor markets where their LFPRs are initially less than half those of natives—producing another fertile breeding ground for violence. Their LFPRs do increase over time but do not converge with natives.  Allowing many of those refugees to instead settle in the United States where they are about as active in the labor market as native-born Americans and usually build themselves out of poverty without much welfare would also decrease the long-term global terrorism risk. 

Syrian refugees could also be valuable foreign intelligence assets, just like many Hungarian, Vietnamese, and Cuban refugees were during the Cold War. As my colleague Patrick Eddington noted, refugees should be especially motivated to help contain ISIS. More accurate intelligence decreases the risks of future terrorist attacks, all else being equal.

Other Policy Changes to Further Reduce the Risks

If the refugee gate is widened, other policy changes can reduce the risk of violent extremism now and in the future as well as the short-term fiscal costs that turn net-positive after 10 to 15 years. Cutting off government welfare benefits for refugees will decrease the public expense and incentivize economic self-sufficiency, self-confidence, and decrease alienation—all character attributes correlated with terrorism. Allowing private sponsorship of refugees is another way to decrease the public risk by outsourcing the monitoring of refugee integration to committed NGOs and individuals spending their own money. Canada has successfully used this strategy and some Senators are now interested.      

Not overreacting to small terrorism risks would aid in the assimilation of immigrants with the same religious background. 


The precautionary principle emphasizes the “better safe than sorry” mentality but shelters us from the reality that nothing is absolutely safe. Risk exists on a spectrum, it is not binary. The fear of high risks and uncertainty should not stop the resettlement of Syrian refugees here, only if a realistic projection that the long-term harms would exceed the long-term benefits should convince the government to further block Syrian refugees. A cold, hard look at the risks and benefits of allowing more Syrian refugees favors a more open policy.