As an active airline captain I welcome law enforcement officers on board my aircraft; after 9/11 it seems to me to have added benefits in case some unstable individual reacts strangely to all the uproar in our country. Unarmed F/A's and Pax might be able to stop an incident but an armed law enforcement officer would really help out!
I have had Secret Servicemen on my flight deck and have enjoyed the experience. They are at least as impressive as any airline pilot I've ever met. As a captain I know that the AA captain had the authority to do what he did, but if he made the wrong call as appears likely then an apology should be made. A mistake on issues like this is understandable in light of all the emotions stemming from 9/11 and will be forgiven. Defending a mistake is just immature. And counterproductive.