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.
For every story I hear about "Police disrupt criminal plan to ..." I hear a hundred about "Police are investigating < fill-in-the-blank crime> committed yesterday...".
If one of them commits a crime or even conspires to commit a crime, they can be imprisoned.
That certainly worked well with Mohammad Atta and his Merrie Band, didn't it?
Perhaps you're planning on hiring John Anderton to do this "good police work". You might want to sign up the Tooth Fairy, too.
And afterwards, we can all have milk and cookies.