So I guess what I'm getting here is (based wholly on the replies thus far) is most of what clans do today is based on preservation of the history and education of others to that history.
Noble purposes, certainly.

But what I'm getting at is this:
Take an indivdual who does not have a so-called "blood line lineage" to a particular clan. That person (for whatever reason) learns about the clan and maybe goes so far to contact the chief of the clan, asking for admission - or at least "permission" to wear that clan's tartan. (After all, even the ancient clans adopted members from different backgrounds.)

If the purpose of the modern clan deals with preservation of history, would there be any reason for the chief to deny the request? Even without the chief's "permission," the kilt is being worn knowledgebly and with respect to the associated clan.

Given that, I'm trying to understand how someone could say "Your daddy's name wasn't McNugget, so you don't have any right to that tartan!"

Again, I mean no disrespect to anyone on this board. But it seems to be a sentiment I occasionally see from some of our UK brethren, and I'm just trying to better understand it.