Not to get into this argument, which I have 'til now successfully avoided, but your comparison is a bit flawed. The Turks and Muslim sub-groups self identify as something other than Turks (Arabs, or Persians or any of the other hundreds of groups), while Qunari never refer to themselves as Kossith. The word Kossith has never even appeared in-game. David Gaider has said many times that Kossith is just a term used by Historians and is no more applicable than 'Bunny-people'. So qunari don't self identify as Kossith, and thus forcing that title on them is actually the opposite of what you no doubt intended (to refers to them as they would themselves).
But anyway, if you really want to hear all sides of this argument do a thread search, there are about 9001 copies of this argument.
I actually don't intend to respect their wishes or self-identification. I hate the Qunari like a five-year-old hates Gargamel. Which is not really fair on my part, or particularly attractive, but we all have our crosses to bear. I call them kossith (sometimes) particularly because it thrills me to stick it to this completely non-existent fantasy culture. (like I said, not attractive)
Dev statements are interesting, but they are, for me, trumped by what I actually see in officially published supplemental material or (much more importantly) the games. For example, David Gaider has said that Morrigan's not an atheist, but she makes what I would consider atheistic arguments with Leliana in a banter. So I think of Morrigan as an atheist.*
Sten states that Vashoth aren't qunari (with a lowercase "q" in subtitles) in a banter. I'm not sure we've seen a Vashoth identify as qunari, either. World of Thedas identifies them as the kossith several times in the section on the Qunari religion. Of Tal-Vashoth, it says "Most are kossith." (129) To me, that's more definitive than a dev statement. I understand others will have differing opinions.
But I will die on this hill. I will never stop occasionally calling them kossith. never
*but I will not get into protracted arguments about this with devs or forumites on the BSN. life's 2 short