Can you clarify your question a little bit? The Kinh ethnic makes up the majority of Vietnamese population, but not 100%. As of 2009, there are around 12 millions Vietnamese who belong to other ethnics. Therefore, it does not make sense to use "Kinh" as an umbrella word for all Vietnamese people. The term "Kinh" definitely came up a lot when discussing ethnic related conflicts and issues though. And as far as I know, there isn't any taboo or controversy using that term in Vietnam.