What. An. Idiot.
And how am I, a traveler at that airport, supposed to know that the gun toting idiot is a peaceful citizen and not a terrorist? Because he's smiling? Because he's white? He obviously has no common sense if he thinks it's a smart thing to do!
If you saw a middle East man with a beard, dressed in robes, walking through the terminal carrying an AR-15, would you just sit back and sigh a relief at that peaceful citizen protecting you? What if it were a young black man dressed in low-slung jeans wearing a T-shirt of some rap group? He may be the most peaceful citizen in existence, but would you ignore the AR-15 he's carrying? After all, it's his right.
Would you approach him and insist he leave and store his rifle in his car?
You do realize that this is in the unsecured part of the airport, don’t you?
If he had a case, such as a golf bag, or a gym bag, that could contain a rifle or sub-machine gun, or numerous pistols, would you feel better? They could be brought into play as quickly and easily as a slung rifle.
Unless and until someone carrying a firearm shows an intent to use it illegally, they DO have the right to carry, regardless of personal appearance.