Gee, Pete, don't knock the tartans. Selling of the "ancestral" cloth and accoutrements puts food on the table for a lot of people.
National Public Radio, in the States, was one of the purveyors of the Twa soldiers in the Jacobite Rebellion legend. Their program convinced American and Canadian viewers of the truth of the story. It is perhaps the best known story about a song. The Gringo and the Rosie legends are two more with wide currency.
They might not generate as much heat as the argument over Celtic-Seltic-Keltic-whatever (which is carried out on several levels) but once a story is accepted, people vehemently object to its displacement. Remonstration becomes a personal attack.