Spaw, I agree with you, what good is a pin that doesn't fasten? Its function is purely decorative, it is just one of these things. Sartorially it would be a faux pas of the grossest sort to actually fasten your kilt with the pin. (NB correct application of split infinitive there btw)

It is like the "sghian dhu" (sp?) the knife, or "dirk" which we wear tucked into our "hose" (knee length socks), when we wear the kilt. This is purely ceremonial nowadays, although it had a functional origin, being used in days of yore to gut, or "gralloch" deer, and to dispatch stray Englishmen.

Murray