It is saddening that this is even a discussion topic today.

The huge number of ethical concerns of this policy are obvious but what does the field of Data Science have to say on this?

We are much better at predicting the future behaviour of individuals based on the what they have done in the past.

According to the FBI, before Ahmad Khan Rahami planted bombs in New York and New Jersey he bought bomb-making materials on eBay, linked to jihad-related videos from his public social-media account and was looked into by law enforcement agents.

How useful, as a tool for prediction, would knowledge of Ahmad's religion have been in comparison to his online activity?  (Answer: Absolutely useless!)

In a world with vast and disparate streams of data from sources including social media, GPS devices, video feeds, travel and credit-card records, demographic information such as religious background has no role as a tool for prediction.

The data is already there to analyse, there is no need to encourage xenophobia as well. Would Trump use a sledgehammer to change a tyre?