No serious person believes ballistic missile defense works. This isn't a fringe belief. There was a major movie with this theme released last year.

Isn't this a different thing? I tend to assume when someone is talking about ballistic missile defense, they are thinking of ICBMs. A House of Dynamite is an example of that. But that seems substantially different from the regional missile defense that seems much more effective. Mach 5 is pretty fast, but Mach 25 is considerably faster.

The lay public is almost certainly unaware that perfect, nation scale ICBM defense is fucking impossible. At least in the US.

People in Israel are probably more accustomed to what a "High but not perfect" interception rate means.

But people in the US are just really dumb about things. They probably think it just needs "Enough money" or "A breakthrough" as if that's just a magic spell you can cast to get around physics.

However, modern anti-ballistic missile defense systems are effective enough that if you spend enough money you can defeat, with high probability, half to most of the incoming weapons. It involves firing many many interceptors against each incoming threat. It does not scale.

This is why it is generally deployed as a way to blunt, possibly not even defeat a North Korean nuclear attack. Nothing more.

Shorter range ballistic missiles suck. They still have the crazy high velocity terminal phase, but they are way cheaper to produce. I don't think it's possible to defend against them economically.