A gun is a technological marvel of a thing. Scientifically they are really very interesting. How they work is kind of ingenious, and their history and how they have so drastically changed the course of all history is fascinating.
I don't want to say that these people probably are all in that boat. But being a gun nut who wants to shoot someone isn't the only reason to find something interesting. I feel the same way about fireworks and nuclear bombs. Looking at the work that had to be done by so many people in order to make a nuclear bomb and calculate what it would and could do? That's as cool and intriguing as a space shuttle or an oil rig drill.