The existence of Arrow means that the only way Iran could successfully hit Israel with a nuke via missile would be to simultaneously (or nearly so) launch several dozen missiles each equipped with a nuclear warhead. Most of these would be shot down by Arrow but at least one would probably land in Israel and detonate.
Well, that's one way to overcome Israeli missile defenses.
Another way would be to fire the missiles from farther away, because longer-range ballistic missiles come in at faster speeds, which would likely exceed the capacity of the Israeli system to track the incoming round.
One can't move Iran farther from Israel, of course.
But that's where Iran's Axis of Evil charter member North Korean comes in:
I've long worried that a nuclear deal with Iran will fail to consider that Iran is likely outsourcing some parts of their nuclear program. But what if I'm thinking small?
What if North Korea sells Iran nuclear missiles and rents the facilities in North Korea to launch them?
From North Korea, these missiles could reach Europe, Israel, Turkey, Saudi Arabia, Egypt, Pakistan, and a number of targets in America. So Iran doesn't need to have the missiles inside Iran, really.
Consider that Iranian missiles fired from North Korea would offer advantages for Iran.
Missile defenses in the Middle East and Europe are designed to handle relatively short range missiles fired from Iran. Those missile defenses cannot handle the longer-ranged ICBMs that will plummet to their targets at a speed too high for those systems to handle.
Unless I'm just being ridiculous in speculating on this, of course.
But I'll keep repeating this caution: The Iranians are nutballs--they aren't stupid.
Don't underestimate Iran's ingenuity. That's worse than over-estimating their desire to cooperate with us and become a responsible regional power.