Wouldn't the best-case scenario be, if Iran launched nukes at Israel, to detonate their own missles over their own territory? How ironic that would be. And sublime justice.
Yup, that would be better. But I am pretty sure that Israel only has missile defenses for the terminal phase of a missile attack. Their systems can't reach a missile launching in Iran, think about what it would take to detect a launch at that distance and how fast the intercept missile would have to travel to reach the target before it left Iranian airspace. Their only choice is to track the incoming targets and fire their interceptors to meet them on the way down.