I'm not sure I understand why a simple ultimatum to any of the rogue countries developing nuclear weapons isn't our only valid defense against them.

Here's that ultimatum:

Should your country verifiably attack another country of the world with a nuclear weapon, the United States (and if we could get their cooperation on this - Russia) would unleash a massive nuclear attack on you which will reduce all your major cities to glass and destroy a substantial portion of your population. The primary targets would be the centers of government and military. Martyrdom will no longer exist in your country because to be a martyr there have to be followers remaining. We will ensure that is not the case.

Seems with that policy, which kept us immune from nuclear attack from the Soviets and Chinese with huge nuclear arsenals, that countries are the least of our worries. Obviously, this strategy is a bit tougher to invoke if the attack comes from a rogue terrorist group not affiliated with a country or government. There's where our emphasis on prevention needs to be.