Why is dont kill civilians such a hot take?

It's largely the Evangelicals' fault. They hold enormous political power, and they think that the world will end when a Jewish state controls Israel. They want to sacrifice some 7 million Jews so they can all go to Heaven and leave the rest of us to rot. So they've built this gigantic political apparatus for justifying or downplaying everything Israel does and cynically employing accusations of antisemitism against anyone who wants it to stop.