I can certainly appreciate a Scot's allegiance to the tartan of his clan, and can well understand the Scottish insistence on a kilt being made only of that material. But Scots clans have tartans to call their own and the Irish really do not. While there are tartans associated with the various Irish counties (and by that I mean all 32 of them) those tartans are not identified with any families very closely. [The "Irish Disapora" tartan or the "All Ireland" tartans are recent -- I'd say artificial -- creations.] So it is common for an Irish kilt to be in a plain colors -- dark green and saffron are the most common. No one would reasonably suggest that the wearing of such a kilt (mine is dark green) is any insult to "the sanctified ancestral costume of hundreds of years of Scots." My family goes back time out of mind in Mayo, fought through its generations for a free Ireland and is a sanctified as any.
Folks may only know of Scottish kilts and tartans, but that doesn't mean those are the only authentic kilts. (Thankfully we live in a wondrous age, when ignorance can be put to flight with just a few taps of the keyboard. (Albeit wisdom still has to be acquired in the old way.)) If you state "it had always been my assumption that a kilt was to be made of Tartan fabric that represented a specific Clan, be it a Scottish Clan or a Celtic Clan," then you are simply wrong. There's no shame in being wrong, unless you persist in being wrong after better information comes along.
Perhaps this lack of clan association with a particular tartan is the reason I find no offense in a black or khaki kilt, as it's not so different from any solid colored kilt. But, to the larger point, I certainly wouldn't broadly and snidely insult someone I'd never met if he chose to wear one. [And not for nothing, some Highlander regiments DID in fact wear khaki kilt aprons for parade and for battle.]
But then, many folks sadly find it easy in these days to talk about things like a sanctified family honor, and to hurl insults, from behind the anonymity of a computer screen. It is one tragedy of the modern age.
philobedoe, my "reaction to your comments" was precisely the reaction a man who hurls insults ought to have expected. (You did expect it, didn't you? Or have you grown so accustomed to your stint as a keyboard bad-ass that you expect, instead, to insult someone you've never met, and have them thank you for the favor? What special sort of craven fellow is it, who instigates such an exchange, then fusses when he gets the expected reply.)
As for any "implicit threat of physical violence," I'll say two things: First, if ever make a threat -- a thin I rarely do, as it wastes breath and gives the other fellow a warning -- there's not single damned implicit thing about it -- so you must have been mistaken. Second, now that you have brought it up, it does seem to me that people had better manners when communication was face-to-face, and a man checked his sneering insults of another man, unless he was ready expected to stand for what he said and to answer for it.
I know -- I'm speaking of things beyond your ken. So please, I'm sure you'd like the last snide little word. . . have at it.