Comment by wat10000

$13 million to save a few city blocks is good. But it won’t be $13 million. You station an interceptor, and attack is so much cheaper, so they’ll add a second attacker. Now it’s $26 million to save those blocks. Still a good deal. Except now they’ll send three missiles. Extrapolate until one of you is unwilling or unable to spend more. (And this isn’t even getting into interception success rates or the fact that an attacker can attack anywhere but a defender needs to defend everywhere, both of which make it worse than one interceptor to shoot down one missile.) Hence this equation only works out for the defender if the attacker is much less willing or able to spend. It works pretty well for Israel versus militants, or for US versus North Korea. It starts to break down a bit when the adversary is even as capable as Iran, let alone anything like a peer.