I suspect cooler heads did IN FACT weigh the probability and negate any shooting down. I give them credit for this as it is their job and they made the right decision.
Black and white shootdown policy should never be adopted. Sane, cool, trained minds, must evaluate first, not react without thought.
What is there to think about? We know that terrorist organizations are targeting this country. We know that they are quite adept at coming up new and innovative ways to strike. We know that there is a very real threat of a small amount of a substance like anthrax or ricin being sprayed over densely populated areas from small planes. We know that that the area of the White House and Capitol is a particularly big target. We know that there is a NO FLY ZONE that begins 15 miles outside of this area. We know that the plane was not responding to calls to divert it's course and got to within 3 miles of the White House.
Frankly, I find it absolutely amazing that we know all of this stuff and the idiots in the plane were able to get out of the situation with their lives. Good for them, but had they been shot down I would not have been surprised nor would I have had a problem with it.