Lucky, major kudos to you for standing up to this jerk!!!
Aside from the arrogance/incompetence issue, the thing that really stands out with me is the threat of security to enforce a business dispute where there is no violence or other need to escalate to a law enforcement response.
This is yet another example of the post 9/11 attitude of some airline employees that they can threaten any pax who dares to complain or call them on substandard performance.
IMHO, I'd skip the compensation request in my letter to WHQ and focus on the liablity issue that could have been had you actually been detained/arrested. If I were GT, I'd be jumping out of my skin after reading this employee's response to the new "focus on the customer."