Project Pluto was abandoned for many other reasons too. Cruize missiles didn't have to be powered by a nuclear ramjet. Although at the time there was no defenc

Project Pluto was abandoned for many other reasons too. Cruize missiles didn't have to be powered by a nuclear ramjet. Although at the time there was no defence against them, there is now. Developing it will be expensive, and the system will have a rather low hit rate, but modern electronically scanned radars, UAVs and AI-based target detection can easily be tuned to take down cruize missiles regardless of the payload.