I don't think it is possible for the Intelligence Agencies and Law Enforcemnt Agencies to keep track of the tens of thousands of people who are a danger to us.
Yeah, they’re too busy worrying about Donald Trump Jr colluding with the Russians.
The wisest move for a relatively open land like America is to keep a culture such that those who want to cooperate will fit in, while those who don’t will find it uncomfortable enough that they won’t want to make it home.
In the case of our present illegale situation, it’s the difference between having charming Chinatowns and having the whole place feeling it has to bow down to learn to speak Chinese rather than English.