"Oh, look, those people aren't obeying the law! If we do things as bad as their worst, things will get better!"
Do you think the Germans would have surrendered if they were certain that every thing they had done to the Jews would be visited on them? Why wouldn't they fight to the last man, causing each side to pay in millions more deaths?
Netanyahu can be stopped without committing atrocities. Committing atrocities in return just means neither side will have any incentive to stop. The rules of warfare aren't there to protect the weaker side, they're there to give an alternative to fighting until one side or the other is utterly destroyed. And if your response is, "Well, I'm okay with destroying all the fascists," then you first have to identify all the fascists. This isn't something simple like blue eyes or straight hair. Even if you could kill every fascist, that still wouldn't mean that you couldn't have more. The belief isn't genetic.