Because a nuclear armed Iran has MAD (mutually assured destruction) capacity w/ Israel.

Israel will be erased wait and see

Writing under the title "Is a Nuclear Iran Really to Be Feared?" William Pfaff argues that the present Israeli policy is not based on fear of a nuclear attack by Iran (or by an Iranian proxy). "It is calculated to prevent the United States from imposing on Israel a solution to its relationship with the Palestinians. They do not wish a permanent legal frontier dividing them from some new and recognized Palestinian state-a frontier sponsored and also guaranteed by the United States, as well as by international law."

I disagree with Pfaff 's explanation of the Israeli rationale for promoting an attack on Iran, namely, to distract America from a two state solution in Palestine, though I agree that neither Iran nor Israel are genuinely afraid of nuclear attack by the other.

The Israeli concern about Iran becoming a nuclear power is that a nuclear-armed Iran would eliminate the Israeli nuclear deterrent as its only security against conventional attack. As long as Israel can wipe out al ...more

Fear depends on mentality