And, no, I do not agree with your statement regarding the right to defense. The question is a moral one. If a nation's leadership is a military dictatorship and is not elected, does that leadership have justification to order "retalliation" hits? I believe that same claim was made by Hitler's troops in the invasion of Poland!
It is easy to say that a nation has the right of self-defense, but it is difficult to implement such international law and it is even more difficult to distinguish what is really a "preemptive strike" vs. "retalliation".
A counterstrike, especially a nuclear one, launched by Israel will not help the Israelies. In the long term, it damages their legitimacy.