From the Washington Post:
A nuclear Iran could make it tougher for Israel to act against enemies closer to home, a senior Israeli military official said Tuesday, suggesting that regional fallout would be broad should Tehran achieve bomb making capabilities.
Military planning division chief Maj. Gen. Amir Eshel said if Tehran attains atomic weapons, that could constrain Israel from striking Iranian-backed Islamist groups in Lebanon and Gaza, Hezbollah and Hamas.
In other words, Israeli leaders don’t fear an attack. (Others have already said this, and American neocons agree.) Rather they fear that a nuclear Iran could deter Israel from asserting its will in the region. Hezbollah is a “threat” only if Israel again invades Lebanon. Hamas would cease being a threat if the Palestinians in Gaza and the West Bank (and Israel itself) were treated justly.
All of this presumes Iran is working toward acquiring a nuclear weapon (Israel has about 200), but to – to repeat—there is no evidence of this.