Sounds great but in reality this just creates another arms race.
If we build a system that is capable of knocking out all incoming nuclear threats, our adversaries will see this as an offensive threat. If they can't attack us successfully, then we can attack them without concern for a counter attack. Mutually Assured Destruction is broken, and, our adversaries will immediately begin developing weapons systems to defeat the iron dome, if that's what it is called.
The next step in this process would be to develop intelligent delivery systems. China is supposedly already developing a system to put missiles in orbit which can "lurk" in space for years until they are activated for attack. The missiles would then use AI to identify targets and defeat defense systems.
And of course, China and Russia both already have anti-satellite missile systems capable of destroying US military satellites in orbit.
Technology advancements make weapons more effective, but that same technology makes counter-weaponry more effective too.
I suppose the argument is, we have no choice. Russia is developing, and supposedly has already deployed, hypersonic missiles. China has made advances too. Until we solve our geopolitical problems I suppose an arms race is the only option we have.