Why do you think GA is a threat? If you wanted to ban commercial traffic, you may have a point. I might even support you there, since we have demonstrated proof of what a big airliner is capable of.
But trying to restrict GA more than it is is simply silly. I can carry a lot more explosives in a Pinto than I can in a Cirrus and have a lot more penetrating power too.
Now that I think about it we should ban private cars. Cars definitely kill a lot of people and they are the terrorists preferred choice of weapon.