They could only cause problems solvable by more superconducting railguns, so they're a net zero at worst.
> could only cause problems solvable by more superconducting railguns
If the projectile is ferromagnetic, or potentially even just diamagnetic, a defense system involving shaped ultra-high intensity magnetic fields becomes conceivable.
Hopefully they don't cause solar system wide loss of consciousness events.
When you activate the city shield, all your buildings become projectiles.