Though I understand the sentiments of feeling connected by tartan association, and the reasoning people suggest learning a little about the clan who's tartan you've decided to wear, I too feel the need to play devil's advocate here.

So, here's the history of clan ( insert name here) tartan. Once upon a time a mill weaving tartans designed a tartan and needed a name for it. They decided to call it the Clan ( insert name from above here) tartan. It was a pretty tartan, and some time later, the clan chief decided rather that having all his clansmen wearing different tartans he'd adopt this tartan as the clans official tartan. If effect an endorsement of the tartan weavers ability to weave and design. By doing this the clan was now uniform in appearance. Of course the mill owner still owned the right to weave and sell this tartan to anyone, as he was a business owner, and prone to trying to make money any way possible. Even naming a tartan after a clan. I'd call that good marketing.

It's all economic people. This is much a part of the clan/tartan history as anything else the clan might have achieved. So next time the tartan police interigate you tell them you do know the history of the tartan, and relay this story.