What Exit?: Note that protecting a ship and protecting a metropolitan area are two very different things.
If the Saudis need to protect a modest building, there’s ways to do a better (but not perfect*) job. Trying to protect a city of 6 million people with thousands of large, important, structures is something else. That you don’t want your anti-missile system to do more damage than what you’re shooting at also creates issues.
As noted, the speed of a ballistic missile makes everything much, much harder.
I think our experiences over the last couple decades (at least) have shown rather definitively that it’s a lot harder to train people in third-world countries up to a basic level of military competence than we ever expected.
I have heard tons of stories how Saudi (as well as Qatari) officers have come to do officer training in the US as basically a status symbol, collecting per diem that is totally obscene, and totally phoning it in on actually doing any work.
If the French and British do not have this problem, bully for them.
The tongue-in-cheek observation of someone on Facebook was that these Patriot missiles were tasked with defeating ISIS, and what better way to do so than to strike the country that is funding ISIS?
The 2 main problems with these systems (GMD, in particular) is the DoD’s perrenially robust tendency to literally ignore cost vs. benefit once these programs get started. Hitting a bullet with a bullet IS technically feasible and it’s been done under tightly controlled test conditions. But the technological challenges are daunting, not to mention playing the never-ending cat-and-mouse game of countermeasures.
Targeting is the biggest issue. The biggest factor in the targeting game (SBIRS) is an ongoing 40+ year-old Lockheed cash cow that looks like it is finally going to get supplanted in the not-too-distant future. So what we actually have in the BMD arena at this moment is basically an un-finished system that has finally (un-oficially) been declared financially unsupportable. So they will start over. Maybe some of the old system will come forward, maybe not. In any event, we can be certain of one thing: Some tens or twenties or more billions of dollars more will be spent developing something (nobody is really quite sure exactly what) to meet the BMD requirement - which in itself might just turn out to be be a pipe dream after all. Or not. Taxpayers will pay to find out.
Actually, for GMD, discrimination is the biggest issue, for which SBIRS plays an extremely limited role. And the Air Force isn’t moving in from SBIRS because it is financially unsupportable; it’s because the threat to a constellation of a limited number of GEO and HEO satellites has become so great that disaggregation is a better investment… maybe.
I suspect that we may end up with a space based early warning system that is probably pretty survivable, but probably significantly less capable.