Here are my answers to the common stupid reasons for not arming airline :
Stupid Reason #1. Pilots can't be forced to be armed. It should be voluntary.
A #1. Does the same logic apply to other jobs? What about bank security guards" or Secret Service officers? Should they be allowed to keep their jobs if they refuse to carry? I say No, and they should be well-trained.
Stupid Reason #2. We'd be leaving ourselves open to the threat of terrorist infiltration of air marshall ranks.
A #2. Or an ever bigger threat, hijackers impersonating air marshalls. If marshalls are undercover the crew doesn't know who they are. What does a crew person do if they see an armed passenger? Assume they are air marshalls? What if they aren't?
Stupid Reason #3. It seems that some people have had the ability to steal airline uniforms and credentials. Such a successful imposter would be able to take a firearm on a plane.
A #3. What about imposter air marshalls? They don't even have uniforms, they are undercover. How hard can it be to fake an air marshall ID? How does the crew decide between the real air marshall and the fake one who is a suicide bomber?
Stupid Reason #4. Anyone can impersonate a pilot and get a gun on board.
A #4. If the imposter pilot successfully gets on board, is in the cockpit and has total control of the plane already, WHAT DOES HE NEED A GUN FOR?
A Note about Undercover Sky Marshalls:
My argument against undercover sky marshalls is: How are the crew going to know who is a undercover sky marshall and who is an undercover suicide bomber?
Let's say that a hijacker has a gun on board and is spotted by one of the crew. Should they feel safe? What if said hijacker pulls out official (fake) Air Marshall ID and presents it to the crew and says that they need to talk to the pilot because they saw something out of the ordinary in Row 3? And then proceeds to pop the unarmed pilot. And drive it into the Sears Tower. Couldn't happen? Why not?
IMHO, pilots should be forced to carry-- it is a job requirement-- and they should be the only ones to carry. They should also be locked in the cockpit for the duration of the flight. Problem solved
That's one good argument.
Another is cost. Some estimates place the number of skymarshalls required at around 100,000 men. That's 10 divisions worth of troops. The cost of this many marshalls, plus the cost of training them, would be quite a bill. Guess who pays? Yup, the taxpayer AND the airline passenger. It would be cheaper to arm the pilot and copilot, and secure the cockpit door, and make other changes such as installing a system that puts the plane into autopilot during a hijacking which cannot be overriden without a code or signal from the ground or which allows remote control of the jet to steer it away from urban areas.
Captains and officers of passenger liner ships that sailed the oceans used to be armed. Why can't the captains of the air be likewise armed? And arm the bus drivers too.
The proposals that have been made like canceling -curbside check-in or having dump inspections of carry-on bags don't even begin to address the problem, let alone have a whole lot of potential for solving it. Skymarshalls might help, but they'll have all the problems that you mentioned.
I'd feel a lot safer knowing the pilots were armed.