http://www.nytimes.com/2001/09/25/national/25SECU.html
"You'd have to have a tremendous amount of screening and training before I'd ever want to ride as a passenger on an airplane where the pilot was armed," said a senior crash investigator for the National Transportation Safety Board. The investigator, a former commercial airline pilot, added, "Some of these guys are the type that'd be quick to anger without a good basis for it."
Straight from the horses mouth.