Abgd
One of the reasons that the restricted area is so big is to give reaction time to allow the shoot down to happen before the aircraft gets to the most populated areas.
I can't help thinking that a light aircraft attack would be quite low on the terrorists list of effective attack plans but it is a possibility that the authority's cant dismiss.
As usual the members of this forum know better than the authorities but also as usual it is always very easy to be an armchair critic without responsabiltity for providing security in this area.