Retributive strikes are not just wrong in principle, they are self-defeating in practice, if their aim is to stop the killing. They just do not have that effect, short of virtual genocide.
No doubt there are people on both sides who have persuaded theselves that, if they rack up the violence high enough, the other side will be deterred, but it doesn't work. It's not a question so much of high moral ground, it's a matter of acting in a way that has some hope of achieving an end to violence.