This is a very, very short piece of fiction. Less than a thousand words, I would say.
As far as I can recall, it is about two humans who are discussing a war with an alien race, which was devastated by learning about the human concept of suicide. After encountering it for the first time, huge swaths of their population were wiped out, essentially as if the concept is a virus and their brains are unable to resist it?
The end of the story has the two people mourning the introduction of a concept that had similar results on people. They don't say what it is.
I feel like this was posted on the blog of a science fiction or technology writer, along with other short short fiction. But I've googled and cannot find it.