Would you be fine if someone described the troubles in Northern Ireland as ethnic tension, or knowing more about what happened would you use some other description?
Why not? It's a lot more accurate than the usual description of "Protestants and Catholics" while still being simple and clear.
Because it wasn’t purely ethnic in nature with Protestants and Catholics on both sides of the conflict. Trying to summarize it as ethic conflict was therefore also also incorrect. Which why using ethic tensions is so often misleading, it seems appropriate in many situations when it really isn’t.
It's better to summarise the Troubles in Northern Ireland vaguely accurately as "ethnic tensions" than precisely wrongly as a religious war between two schools of Christianity.
Being vaguely accurate on a history test may give partial credit, but the news should to be held to a higher standard.
I can see why an organization that does international journalism would taboo “ethnic tension” on the presumption that there is a lot more to be said in order to capture the events and processed they are reporting on.
Look mom, I'm a journalist now. PayPal me, New York Times.
When we debug, do we tell other engineers that we're solving a "software problem," or do we use qualifiers?
Analogously, the point the article appears to make is that if humans are involved in a civil war, of course there are ethnic tensions.
Because the original cause is often irrelevant. A random spat about land might be what sparks conflict, but ethnic tension is what fuels it and keeps it going. And yes, "ethnic" is a complex word, mixing issues of religion, culture, language, ancestry, "tribe"-level social organization and whatnot. Guess what, these things get mixed up all the time anyway, and having a single word to describe the resulting mess is highly useful. The world is complex. Deal with it.