It is an axiom of criminology that "crime knows no neighborhood." In other words, no place, no population is especially criminogenic. Crimes are committed by individuals who make bad choices.
Anyone who isn't aware of the vastly different crime statistics from one neighborhood to another is ignorant of the facts. It is very true that crimes are committed by individuals, and that they are making bad choices. It is also true that some neighborhoods have much higher densities of bad choice makers.
That is why Dr. Martin Luther King's dream was a world where a person is judged by the content of their character, not the color of their skin.
What Martin Luther King said had nothing to do with neighborhoods.
The basic error, the fundamental fallacy, in dealing with the current influx of refugees is considering masses of people as collectives. Including or excluding groups, tribes, ethnicities, etc., is the wrong way to analyze the question. In point of fact, US immigration policy requires each legal immigrant to prove their case on their own merits.
Wrong. The basic problem is that some of the refugees are probably going to be people who make really bad choices, and, in fact, US immigration policy is inadequate to the task for sorting the good from the bad.
A million years will not be enough time for the terrorists to kill everyone they dislike.
1. Tell that to those already dead (they probably don't care that they are a small part of some larger number.) It would take far, far longer for a single, mass murderer to kill everyone in their country, but that isn't considered a reason for letting him go on killing.
2. Terrorists can be expected to get better at what they do. They will adopt new and more effective technology for killing.
Meanwhile, immigrants to Europe and the USA bring valuable human capital away from ISIL. Immigrants bring enterprise, ingenuity, and initiative.
Some immigrants bring value, some are terrorists or rapists or welfare parasites.
They need actual vetting.
...actual harm is harder to prove
Sometimes it isn't that hard to prove. Look at the Boston bombers.
Civilization will survive ISIL, but only if and to the extent that we embrace a full, consistent liberty....
And defend ourselves. A civilization that doesn't defend itself isn't likely to survive. And liberty is a meaningless term without the defense of individual rights. And actual defense, not just lip-service.