I don't know about the "unusual" characterization; there seem to plenty of otherwise intelligent people posting here who are so afflicted. I guess it is necessary for them to acknowledge that their belief in the ability of guns to act without human intervention before it can be classified as a true phobia, but believing that guns corrode a person's ability to think rationally is close to the same thing.
It's more of a cultural thing here, cemented into the psyche from childhood over a millenia's worth of generations that the "peasantry" or "commoners" shant possess weaponry that would allow them to poach the king's deer or revolt against their "rightful" overlords. It trancends mere brainwashing. With that foundation, it's morphed into today's "Why, they're simply too dangerous. I can defend myself with a niblick if it comes to that..and so should everyone else be forced to". The notion that it's an inherent Right...well, that philosophy just can't be fathomed let alone embraced by anyone still clinging to dusty, old notions like Monarchy and Aristocracy by birthright and that government is something you kneel before seeking favor while it doles out conditions for one's existence.. That's where all the tut-tutting and finger-wagging comes from; if they can't have one ( the Right and/or the weapon), then neither should you.
That's why, to us, it walks like a phobia and talks like a phobia.