Even if the Arrow only has a 50% chance of stopping all attacking missiles, or just a 30% chance, even that is of great value. An assailant will have to worry about the real possibility (even if not certainty) that his effort will fail, or be stunted, and that he will then be subject to Israel's full retaliatory might. Does one expose one's country to a 50% chance, or even just a one in ten chance, of ceasing to exist? Keep the Arrow; retire Reuven Pedatzur.
U.S. defense chief tells Congress: Military options remain against Iran (DPA)
from the article: An alibi for the Arrow