There are two results of this discussion which I think are worth remarking.
First, the safety culture around firearms seems to contrast highly with the safety culture around flying.
Second, there are apparent conflicts of authority in any flight deck in which the captain is not an FFDO and others are.
Both of these features can and likely will result in difficulties at some point.
To the first. There are worries, which have become very prominent recently, about criminalisation of aircraft incidents. Pilots being prosecuted for negligence, gross negligence and so on. Indeed, there is a whole PPRuNe thread about it which is still active, and it has occurred prominently in other threads, such as the Brazilian midair one. That is one side: a wish on the part of some for a safety culture in which neither blame nor related concepts of culpability such as negligence play much of a role, and in which the analysis of systems and their operation takes explicit account of human capabilities and limits.
Then there is the safety culture around firearms, which apparently considers any unwanted discharge of a weapon by its operator/owner to be negligent (as in Negligent Discharge). In other words, safety here is seen to be very connected with the concepts of negligence and blame. Very much zero tolerance, understandably.
An FFDO has to play both contrasting cultures simultaneously. That is not the kind of recipe that allows system safety analysts to rest content.
To the second. The authority of the captain over all others in the operation of hisher aircraft is enshrined in aviation practice since the beginning, and has a much longer history in seafaring. It is a principle that many believe has contributed substantially to the safety of aviation today. It also has known weaknesses, of which the Garuda overrun at Yogyakarta is an example. These weaknesses have been addressed, as in CRM, with some, but not perfect, success.
The FFDO program apparently introduces another authority into any cockpit in which the captain is not an FFDO. That this is an unresolved conflict has been illustrated well by this very discussion.
The FFDO program is not going to go away soon, if ever. Might I therefore suggest to our U.S. colleagues that they think hard about these conflicts, how they might lead to a decrement in overall safety, and what might be effective in ameliorating their influence? I think answers most probably have to come from inside the system itself.
PBL