... Oh wait I get it. "Ethnic" as a noun is a word to be used appropriately by people who actually belong to an ethnic minority, whereas "ethnic" as an adjective is the better/more appropriate choice for those of us who were so "fortunate" as to be born into an ethnic majority family.
Ahem; don't mean to be flippant, cute, or curt here; just bogged down by a mass of PM's, emails, and unanswered posts on various threads, so forgive me for whipping through this bit of honestly intriguing information and filing it in a flash. I promise to say "people from ethnic minorities" instead of "ethnics" from now on.
Oh ... unless it's a casual conversation with people who I know and who know me well, in which case I can make an exception and indulge myself in the use of the word (noun) "ethnics." Whew! I think I've got your basic idea right but am glad to accept any corrections I'm in need of.