I've eventually come to the conclusion that we actually do have to start there - i.e. that morality is based purely in self-interest *.

But so what we then have to do is criticize escalating violence on the grounds that none of us - out of our own self-interest - wants a world where violence continually escalates.

The reason why people have an instinct for wrath and revenge is to ward off future aggression against ourselves. And there is actually legitimate, pragmatic, value to that instinct.

But the problem really starts to arise when we invent imaginary concepts like "justice" to "legitimize" our revenge, and then debate whether one reprisal was "just" or not. And the reason why ideas like "justice" are so dangerous, is because they are ultimately completely made up, which means there are no bounds or rules for what people may claim is "just" or "injust".

But if we just stuck to "self interest", then we could have a sober conversation about it. And we could say to Israel, that it scares us when we see them destroying so much more life and property than was taken from their own people. And we can say to Hamas and any part of the network supporting them, that it also scares the bejeezus out of us when they cut people up and say they want to do the same to every other Jew and non-muslim they can get their hands on.

* https://medium.com/the-panopticon-publication/morality-is-personal-and-tribal-always-20c8c31f5d29