>>63907919the issue comes down to cost versus benefit. say you have a peer nation conflict:
10 interceptors
10 incoming
90% pk for the interceptors
interceptors and incoming cost about the same
1 incoming gets through and hits your defended target anyway. yes, that's better than if all 10 got through, but you expended the same amount in munitions as opfor and you still got hit.
air defense against planes and such is very useful, the same for warships with dual-purpose sam systems (sm-6 being both offensive and defensive), but you get to a point with missile defense where you should just buy more offensive missiles.