By Boaz Barak and Omer Reingold
President Trump had just signed a new executive order revising the prior ban on visitors from seven (now six) muslim-majority countries. It is fundamentally the same, imposing a blanket 90-day ban on entry of people from six countries, with the conditions for lifting the ban depending on the cooperation of these countries’ governments.
One good analysis of the original order called it “malevolence tempered by incompetence”, and indeed the fact that it was incompetently drafted is the main reason why the original ban did not survive court challenges. The new version has obviously been crafted with more input from competent people but it does not change anything about the points we wrote before.
Every country has a duty to protect its citizens and we have never advocated “open borders”. Indeed, as many people who visited or immigrated to the U.S. know, the visa process is already very arduous, and involves extensive vetting. A blanket policy does not make the U.S. safer. In fact, as opposed to individual vetting, it actually removes an element of unpredictability for any group that is planning to carry out a terror attack in the U.S. Moreover this policy (whose first, hastily drafted version was crafted without much input from the intelligence community), is not the result of a careful balancing of the risks and benefits but rather an attempt to fulfill an obviously unconstitutional campaign promise for a “muslim ban” while tailoring it to try to pass it through the courts.
This ban hurts the U.S. and science. Much of progress in science during the 20th century can be attributed to the U.S.’s role in becoming a central hub for scientists, welcoming scientists even from countries that it was in conflict with (including 1930’s Germany and cold-war Soviet Union, and more recently, Iran). This has benefited all the world, but in particular the U.S., which during the 20th century became the world leader in science and technology as a result. Science is not a zero-sum game, and collaborations and interactions are better for all of us. We continue to strenuously object to this ban, and call on all scientists to do the same.
Windows On Theory 
Perhaps the legal incompetence has been alleviated, but the document is still stupid in terms of national security. (I am ignoring the moral issues, or its impact on science, which has been excellently presented above.)
The “justification” is that in these countries the government is unwilling or unable to give the US information about visa applicants that would allow us to vet them properly. This would imply that we have perfect confidence that countries NOT on the list are doing a great job of informing us. Somehow I do not picture Azerbaijan, or Saudi Arabia, or Nigeria as countries with reliable records that help us, honest governments that we can trust to provide us with trustworthy data, and places where we have water-tight assurance that passports were not bought through local criminal organizations. In fact, one can think of a number of countries not on the list where it is hard to distinguish government and local criminal organizations
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Of course, the ban also makes it truly difficult to bring any friends our government may have in these countries to the US, without branding them as US spies.
In other words, the ban does not serve national security. It, like confiscating tweezers at airport checkpoints, is theater. Having to be at the airport hours early, and having to take off our shoes is only an inconvenience. The ban does real damage.