I see what you mean. There are two scenarios here. The warheads are nuclear, or conventional. In the case of the nuclear warheads the successful interceptions have huge value. In the case of the conventional warhead, the shrapnel will decelerate due to the loss of aerodynamic shape/ loss of ballistic coefficient. Also the fast shrapnel could be less dangerous than a larger vehicle hitting at hypersonic speed. We are not counting the personnel here. Usually such expensive strike will occur against buildings, high value targets (personnel inside) and less probably on open field (personnel outside). So, the interception, even against conventional warheads could be valuable.