It is true that Israel believes it needs a nuclear monopoly in its region to ultimately ensure its long term strategic security. It is also true that this Israeli strategic need is the primary motivation for the US to violate the NPT in a way that denies Iran the rights both guaranteed by the treaty and also given with little or no controversy to many other countries including Japan and Brazil.
But it does not follow that the ultimate reason Iran wants to build a "Japan option" - the capability, in theory, to weaponize its nuclear program in an emergency is related to Israel. The reason for that is, primarily, defensive. In simple terms, if Iran has a Japan option, it is safe from regime change led by the US and threats of regime change.
Here we have the Council on Foreign Relation's Ray Takeyh describing this.
... [N]uclear weapons, by definition, are such a narrow category of arms that they can accomplish only a limited set of objectives. They do offer a deterrent capability: unlike Saddam's Iraq, a nuclear Iran would not be invaded, and its leaders would not be deposed.We also have John Bolton saying about the same thing. (Also demonstrating the reflexive habit of Western commentators to deliberately and misleadingly conflate weapons with capability.)
Having that nuclear weapon would make a big difference. For example if Milosevic had had nuclear weapons as Yugoslavia was disintegrating Bosnia, Kosovo could have turned out very differently simply from the threat or the risk that he would use themA Japan option, even without leaving the NPT or building a weapon, gives Iran very real strategic benefits. Takeyh actually describes this as "limited" but he's describing independent protection from regime change, even from military intervention. That is not limited at all, that is a huge benefit.
Stewart: (Interrupting) That we would not intervene if they had them
Exactly. That's why it's so critical to stop Iran from getting nuclear weapons. Once it actually has the capability the equation changes dramatically.
One may ask, "can't the US offer economic incentives to compensate Iran for giving that up?" Keep in mind now that what the US would be asking Iran to give up is a huge strategic advantage. It is a mistake to think of Iran's nuclear program primarily in terms of the threat it poses to Israel. As a side effect, Iran's program threatens Israel's strategic position but it primarily deters US and foreign attacks on Iran's own sovereignty.
So for this huge strategic advantage that the US would ask Iran to relinquish, the US cannot offer huge rewards because Iran still does not accept Israel, still acts to weaken Israel's position. If the US was to offer to end all sanctions in exchange for Iran giving up domestic enrichment, or keeping its LEU stock permanently below the threshold necessary in theory for a weapon, and Iran was to accept that, Iran would both be giving up a large amount of its security and at the same time would become more of a threat to Israel.
If the sanctions were to be lifted for the nuclear issue, Iran would have more resources that it could use to strengthen the positions of Palestinians in Gaza and the already intolerably fast build-up of Lebanon as a military force. An Iran without sanctions would be far more dominant in Iraq and would have resources to do some "democracy promotion" in Jordan, Egypt and Saudi Arabia that would be good for the people of those countries but would destroy the colonial structure the US holds in place and that is also critical for Israel's survival.
The United States is severely limited in what it can offer Iran to end its nuclear program while at the same time Iran's nuclear program has great defensive value that Westerners do not even realize they admit to. Because of this, we are not going to see a nuclear deal that satisfies the US and Iran at the same time, at least until the US decides that the status quo is worse than accepting Iran's nuclear capability or manages to install a new Shah in Iran.