I think you're missing the point that spending trillions for a boost phase intercept system (even if it worked) has a massive opportunity cost. A diamond door (or gold!) is a terrible investment if adversaries can bypass it through an open window. There is an opportunity cost, not just for balanced security, but also social and economic costs.
But boost intercept doesn't even meaningfully reduce ICBM threats.. adversaries simply build the bypasses that render the "shield" useless. Offense is always easier and cheaper than defense for this sort of system. ASATs, decoys, cyber, jamming are all low hanging fruit. Sending large synchronized volleys is an easy way to exploit GD's interceptor absentee problem (which is approx 1000x worse than a regional system like Iron Dome).
This all amplifies the false premise that the "shield" will work flawlessly, because if you're going to destabilize MAD you better get it right. The fact is interceptors are not even single 9's in the real world with countermeasures, and a Tesla FSD attempt v420.69 doesn't cut it for nuclear war. (Oh don't worry we'll push a patch and next time we won't lose Chicago!)
And like I said, everyone knows this isn't a defense system for those reasons and more. Golden Dome's satellite architecture is effectively an orbital weapons platform capable of offensive global strikes, which fundamentally destabilizes geopolitics. If you're an engineer working on that you better have your eyes wide open and be able to explain why you think this is a good thing.
For some history, the very first contract SpaceX ever got was for https://wikipedia.org/wiki/DARPA_Falcon_Project a global strike weapons system.