Okay, I get that it is illegal to bring a gun onto a plane (although, I think this should be a decision made by airlines/airports, not the feds). But, people forget about contraband all the time when going to the airport. Usually, traveling means you have about 500 things on your mind. Is it really necessary to arrest an otherwise law-abiding citizen with a legal right to carry a gun for forgetting to take it out of his backpack. I mean, if he had remembered, it's really easy to check an unloaded firearm when you check in for your flight. And, does the TSA really think that someone would be stupid enough to put the gun in a bag and then put the bag on the x-ray belt?
Give the guy a warning, make him check his gun, and send him on his way! This guy is not a terrorist, so why does our government insist on treating him that way?