Fine, how were our security people suppose to confirm that was the case? Stip out extras to add capability. Did the have a full tank, or only enough to reach DC - one way trip? Or may be even the much talked about 'suitcase nuke' Too many what ifs to ignore.Add to that the symbolism of a strike even w/o explosives.
Those supposed "suitcase nukes" are more sci-fiction than real. They weigh several hundred pounds.
They didn't know what this plane was gonna do... but the point is, they judged the situation correctly in this case. It's not an easy call.
Big terrorist attacks don't bring this country down, piddly vandalistic ones wouldn't either, And that's good news, because eventually, something will happen again that's real. It can't be prevented. Many many good people will try, and often succeed in stopping, deterring and foiling attacks. They will also have to deal with a lot of scares that aren't really attacks. Myself, I pray for their continued wisdom and luck. I'll not fire the lot of them and change all the protocols because a couple of people looked funny running on TV.