Require all those who want to saw of the heads of Infidels to wear a special armband?
DuncanWaring wrote: "How do you distinguish those who want to saw your head off from those who don't?"
The same way we identify other criminals from law-abiding citizens--good police work. If one of them commits a crime or even conspires to commit a crime, they can be imprisoned.
To think we could even identify every Muslim in this country, much less incarcerate or deport all of them, is ridiculous. What we do have the capability to do is the necessary HUMINT to identify and destroy violent Muslim groups.