Wow,
Been gone awhile and all the fun topic pop up!

I'm not going to debate the legality, need or responsibility that comes with carrying a knife.

But to get back to the nature of sgian dubh, there is a question with translation. While "black knife" mean a black handled knife, reflecting the wood that it was supposedly made of, there are arguments that "black" really meant "secret." The knife was worn hidden, then transferred to the sock when among friends - so that it was visible.
Given that there are more modern versions of kilts - I would argue that a typical folding knife - spyderco, emerson, cold steel, etc. are the logical descendants of that noble knife.

Yes, if I wear a "traditional" sgian dubh, I want it to be functional. But if I want function, I won't turn to a sgian dubh in my sock.