Iran is not suicidal - they're not going to "nuke Israel", and even if they did, "one nuke" won't come close to ending Israel forever.
Israel has second-strike capability, both from ground silos and from submarines. A nuclear attack on Israel would guarantee an automatic nuclear response against Iran.
Israel's nukes are modern thermonuclear fusion bombs - "H-bombs" - which are magnitudes more powerful than anything Iran is close to building. Not to mention the other 3 nuclear powers within 200 miles of Iran.
If a country behaves in a rational manner,,, your argument might work
Iran, or least it leaders are far from stable and trustworthy.
If a theocracy has a belief that suicidal acts can get one into heaven,
it seems a hard sell to believe they are not at least a bit irrational.
Besides, a nuclear bomb capability is the required "trigger" for a H bomb
so, yeah it is a big thing