Any deterrent affect would be minimal. MAD depended on the Soviets being basically rational. The leadership of the hard line countries and their so called freelance allies aren't rational. However, it might give some of them pause, particularly the possibility of the holy sites being destroyed.
However, I'm not interested in deterrence, if this were to happen. This is a declaration of principle to the whole world so that they will understand what we do when we do it, under those specific set of circumstances. I'm not arguing for "deterring" anything after they've used nukes. I'm eliminating all possibility of anyone from there ever having the capability of setting it up again. If they're all dead, innocent and guilty, then there's no one left to make it happen.
That act might then have a deterrent affect on any remaining rational actors elsewhere.
Al Qaeda hates Saudi Arabia, they hate Egypt, they hate Jordan. Why wouldn't they make something happen that not only takes out the ruling regimes to usher in their own? Much of "street Islam" will cheer them.
You said -- "However, I'm not interested in deterrence, if this were to happen. This is a declaration of principle to the whole world so that they will understand what we do when we do it, under those specific set of circumstances. I'm not arguing for "deterring" anything after they've used nukes. I'm eliminating all possibility of anyone from there ever having the capability of setting it up again. If they're all dead, innocent and guilty, then there's no one left to make it happen."
Well, I've advocated all along a "war on Islam" -- in order to totally eliminate it from the world and make it illegal everywhere you find it. If we can't do that -- then we are going to be cursed with Islamic terrorist until "Kingdom come". And that won't be too much longer anyway...
Regards,
Star Traveler