"All family members should also be repatriated to their country of origin without appeal.Perhaps this threat on them,for a change,might focus the minds of the parents on what their children are plotting."
I thought the first bit of your post, "...any person who enjoys the hospitality of this country will forfeit that right if they engage in any terrorist related acts..." was fine. The above extension isn't. You don't have to be plotting anything evil to keep a secret from your parents. It's not irresponsible parenting to be unaware of everything your child is doing, so the family can't be held as guilty and so deported. That would be going far, far too far. Sadly in this case children are keeping the worst kind of secret from their parents -- but this isn't the fault of the parents for being unaware by any means. By the time children are plotting terrorist acts they're usually of an age where the parents should be taking a reduced responsibility for them anyway.