1) The letter was pompous and arrogant, and assumed that the SECDEF works for Congress, and thus could be ordered about like some "staff member."
2) As mentioned, they were AWC students, and had a perfectly valid reason for being in attendance; that's the only answer that needs to be provided to this jerk. The question is, when the writer is informed that it was a part of continuing military education, will he apologize?
3) Here's where I'm going to get myself in trouble: Each of you, having seen such a group of military people viewing a congressional meeting, should be asking the same question this idjit did: Why are they here? Are they spending time viewing Congress when they should be working budget and manning issues? If they had been "flag officers," we pay those guys a lot of money each year; not to mention that each flag officer does usually have at least one aide/exec, and sometimes an enlisted aide as well. So at a time when at least our Air Force is being asked to reduce its manpower 30,000 personnel, what were these guys doing? Should we be reducing our manpower by their slots?
In my opinion, the gentleman was correct in asking for accountability. The way he did it, was not.