Any gun that someone wishes to own for purposes other than shooting it or making an immediate profit...the human desire to collect is intriguing in itself and will drive otherwise sane, balanced well adjusted people to run up debt, break the law and become a recluse.
Airguns are nothing compared with some secret hobbies I have been surprised to discover amongst acquaintances - Victorian pornography, unicorns, fossilized poo, bullet heads/musket balls that have passed through a human body, tanks, owl pellets and school text book graffiti being the less worrying ones!
Now I'm off to fit another couple of cabinets to the wall
"But we have our own dream and our own task. We are with Europe, but not of it. We are linked, but not comprised. We are interested and associated, but not absorbed."
Winston Churchill 1930