Tartans (unlike coats of arms) are usually intended to be worn by more than one individual at a time, most being intended for entire clans or names; yet the situation of entitlement vs. capability is almost identical. Anyone is capable of assuming a coat of arms, but not all those who assume a particular coat of arms are actually entitled to bear them.
"Almost identical"? They're completely different. Where there is a legal entitlement to arms, there is none for tartan. There never was. The tartans themselves did not originate from any sense of entitlement whatsoever, and comparing it to something that did and calling it "almost identical" is stretching things quite a bit.

The idea of tartan being restricted to certain surnames is nothing more than a recent tradition (less than two centuries old), which was never universally practiced in any time period, and is only observed by a few romanticists who want tartan to mean something other than what it originally did.

And while I fully respect the idea of clan tartans having some meaning to people and offering a sense of connection to kin, I think it's important to be truthful and objective in relaying to others the history of tartan, instead of trying to push a narrow, romanticized, mythical agenda.

Myself, I wear only one tartan: the clan of my mother. And I am even taking steps to adopt her name (although the reason has nothing to do with tartan affiliation) which would put me in full compliance with Mr. Mackinnon's advice. But at the end of the day, I don't really care what he thinks is 'correct' or not. Just because he wrote it down doesn't make him the authority; nor is his opinion the final word. Plenty of other historians disagree with him. I wear the tartan I have blood ties to, which has absolutely nothing to do with what my last name is.