Norms are violated all the time to very little consequence, sure, this would be on a whole other level but what could you do… what could anyone do… and that’s the point. I think people are over optimistic about the potential for collective action. I’m not the person who needs convincing that it’s a bad idea, that decision maker is in the government somewhere.
This is bizarrely confused, in fact thousands of analysts have already studied the details of such a system since the 60s: https://en.wikipedia.org/wiki/Fractional_Orbital_Bombardment...
It has too many downsides to make sense to deploy.
The only scenario where it can do anything meaningful is if it's immediately used, then MAD would apply just the same.
I can't parse the rest of the comment, so I would advise you read up on the historical background if your as confused as it seems.
A substantial fraction of the folks in Ottawa would defect after such an extreme violation of norms, let alone in any other capital.