I'm currently reading Alan Dean Foster's Founding of the Commonwealth series. Specifically, right now I'm on volume three, Diuturnity's Dawn, which has various fanatic, xenophobic factions among both human and thranx planning terrorist acts to try to prevent the birth of what will become the Humanx Commonwealth. There comes a point at which the human and thranx xenophobes meet each other.
At first, it made my brain hurt to try to think of the sheer broken-mindedness and mental contortions necessary for opposing groups of human and thranx fanatics to cooperate and work together with each other to try to prevent the possibility of humans and thranx ever cooperating and working together with each other. But then I took a mental step back and thought about the broken-mindedness that makes its presence known almost every day, all over our world.
And suddenly, it really didn't seem that big of a leap any more.
(Naturally, it goes almost without saying that both groups are planning to backstab the other as soon as their respective dastardly deeds are done.)