I spent a large number of years in the real wild, wild west - Africa, and throughout that time I carried my SIG P226 24/7 and depending on what I was doing would have one or other of my weapons - an HK53, MP5K and a Sites Spectre - on or close to me most of the time.
In the mid 80s, Nigeria - where we were nominally based - was effectively lawless. As a Nigerian flagged airline, we could not get credit for fuel, handling, landing etc and that, coupled with our habit of buying our own (usually perishable) cargoes for return flights meant that our crews would be carrying very large sums of money. The local 'rogues' were well aware of this, and as a result our crews along with those of other airlines were targetted.
I was personally involved in a couple of firefights which I can assure anyone who has never had the experience of being under fire is definitely something you want to have on your 'must miss' list. In addition, to know that you have taken someone's life perhaps microseconds ahead of them taking yours is a gutwrenching experience.
In order to remain competent with my firearms, I must have spent thousands of dollars on many tens of thousands of rounds on target practice at least twice a week. Practicing as well being able to draw my SIG in a variety of situations and positions. Stripping and cleaning all of the weapons on a daily basis. Driving around town with my SIG under my thigh, and the MP5 on the seat next to me, covered by a newspaper.
Having a firearm is a whole different way of life. It's not something that you can simply have as a piece of kit; an item on a checklist: "Cabin secure; seatbelts on; S&W 38s loaded and safety on..." - it's a mindset. In order to be fully effective, you need to be carrying 24/7 so that you feel naked without it and of course that's just not practical here in the UK (or most other places) for your average airline pilot.
And think of the paperwork. We had piles and piles of the stuff - consents from the Nigerian CAA; special customs forms, declarations, licences ... Add to that the practice and training time, and your worldload has increased substantially.
For what it's worth, the majority of pilots I know don't have - in my opinion - the capability to deliberately draw down on and kill another human being. (And that's a compliment, by the way).
No. Flight crews need to concentrate on getting the aircraft down safely in a situation from behind the safety of an armoured door (which with Kevlar and other ballistic nylons is not something which would add huge amounts of weight - we're not talking six inch armour plate here!); and let professionals deal with the inflight security.