Historically in the U.S. pilots flying the U.S. Mail were required to be armed, as was anyone else with custody of the mails.
The state law in Alaska is interesting and I understand causes problems sometimes when an aircraft flies from Alaska to Canada and lands in Canada while carrying a (God Forbid!) rifle.
Some kind of security is needed for aircraft and aviation. Practically speaking I do not believe the pilot/copilot should be required to "ride shotgun" as in the old west of our Hollywood fantasies because it would distract from other pilot duties and result, overall, in a less safe situation. Armed law enforcement personnel, properly trained, could fly on more aircraft, better security on people and cargo coming on the aircraft and the servicing and maintenance areas will be needed. It will all cost money and the passengers/cargo shippers will have to pay for it.
Bright side is there will be no more air rage incidents. How much air rage does El Al have?