Who is arguing that Israel fighting back is wrong?

Most of the world thinks that. They would also take issue with you characterizing what Israel is doing as "fighting back" and "self defense". Self-defense is when you steal land, ethnically cleanse the inhabitants, force them into a small area, then besiege them there for decades, and then blow the whole place up. Because some of them dared take up arms and broke out. You know, self defense!