I see. We do have good systems, but too few to be of practical relevance in most threat situations.
The North Korea case shows that the step from having one missile to having 100 is extremely short compared to going from having no missiles to having one missile.
I don't think that's a consensus view? Jeffrey Lewis says the opposite,
- "The point is that North Korea is clearly aimed at overwhelming the US missile defense system in Alaska... At that cost, I am pretty sure North Korea can add warheads faster than we can add interceptors."
> even if they got one through, wouldn't North Korea basically be a wasteland 30 minutes later
The idea is if to have a credible threat to keep us from acting first, as well as giving many countries a vested interest in the stability of the regime: if the Kims go, North Korea goes, and so does somebody else.
Congratz, you grasped the facet of MAD that is unacceptable losses - for the US a single warhead getting through is too high a price to destroy pretty much anyone.
The North Korea case shows that the step from having one missile to having 100 is extremely short compared to going from having no missiles to having one missile.