Legal immigrants commit crimes at a lower rate than U.S. citizens, and illegal immigrants at an even lower rate than legal immigrants[1]. This should not be surprising. Those who are in a country illegally know they will likely be deported if caught committing a crime.

Why build apparatus to monitor the people least likely to commit crimes? In isolation, it doesn't make sense. If you take a look at other actions the Trump is administration is taking, such as cracking down on universities in ways designed to suppress protest, it becomes a little more clear. This database will likely be extended to cover citizens as well as immigrants, and not for the purpose of preventing crime.