That's not really what the report is relying on. It's saying having a system of detections and interception satellites which can catch ~100 missiles forces the stakes to be more "all out or nothing" from large scale threats and "fully preventative" for small scale threats (e.g. North Korea). It also considers the satellite layer 1 of 3 layers that help achieve that small escalation prevention goal.

Nowhere does the report claim a Starlink type satellite layer would be or would need to be untouchable in a full scale WW3 scenario.