Rapid decompression. Years ago I worked at an Aeromedical Research Lab on an Air Force Base, and their outer-space studies proved that an astronaut had three minutes to react if his spacesuit was pierced.
Although the atmospheric differences between outer-space and 30,000 feet would be somewhat different, the same principles apply. Once the outside pressure equalized with the inside pressure, the lack of oxygen would be the only major concern. That's why those little oxygen mask thingy's drop down. Unlike in the movies, a single bullet hole does not result in a row of seats being sucked out.
As for the pilots complaints about having armed agents on board who have to pass less strenuous tests than they is required of them, I agree with their complaint.
OTOH, if the door to the captains' cabins have been upgraded so that they are impenetrable, then the captains have little grounds for complaints.
The bottom line that even our homeland security seems to miss is that 9-11 will never happen again. Passengers will never again sit idly by, believing their captors that they will be safe. Passengers will attack en masse, believing that if they are destined to go down, they will at least go down fighting.
And if a few unknown passengers are carrying, then all the better, because it is the unknown element that might deter future attempts.
Excepting, perhaps, for a hijack of an almost-empty plane.
From the standpoint of the federal gov't, this has nothing to with people flying armed who have passed strenous tests and background checks.
If it did, they would allow private citizens who could pass similar tests to fly armed.
Rather, it has everything to do with increasing the disparity between the almighty federal goverment and us lowly peasants.
So do I, on general principals.
But nobody seems to have addressed the biggest question that this thread has posed: Why the hell do Dept of Education and EPA (!!!) officials need to carry a concealed weapon?