You have to think about this kids logic. If he had wanted to kill someone up to and including himself with an aircraft, why take the Cessna 172? We can see in that pic he only wasted one window. I figure he just wanted to go out with a bang.
But, still, he was a moron. He took a light plane and crashed into a building to make a point. What it is, I don't know, but he obviously wanted something more than to just die. But, in situations like his, you have to put yourself in the Coast Guard's and military's shoes. These guys had no idea that this kid planned on flying into a building. They didn't know he was suicidal. Their job was to get the aircraft and pilot down and avoid casualties.
What if the military hand snubbed this kid? Then we'd have people saying, "But, he had his whole life ahead of him. He was so young." because that's where our society has come to. No one would have cared if they shot him down becasue he was a threat. There'd be someone out there who'd be crying to the military for killing an innocent student.
Now, here's my opinion. Yes, I do think the military should have turned that plane into a wisp of smoke, and that they should have done it after the kid never responded. But, thankfully no one was hurt, and the only thing damaged was one window and an office.
And yes, I am also afraid of "copy-cats" wanting to be famous by driving a light plane into their school or something. I've heard ideas being thrown around here at school, being as my high school is less than 5 miles from Meachem Airfield, where their is a flight school. I'm a little worried, but I doubt anyone is dumb enough to do something like that again...