1rovert,
And if they checked you out, I am sure you would pass.
The 7/7 bombers were born here, the Paris and Brussels bombers were home grown.
What has happened is that third and fourth generation immigrants, whose parents and grandparents appreciated the sanctuary and opportunities of being allowed to live here, those present descendants have become radicalised and are rejecting our way of life.
There are many reasons for that, but no amount of checking their families, or background checks will work. The natire of those radicalised, is that no one knows until they commit an act of terrorism.
I realise that I am saying there may be 50, 100 or more terrorist waiting to attack us, but locking up 2 million muslims (even if it were pissible, and it isn't), would not find them and stop them.