Starlink doesn't replace fiber. The amount of bandwidth Starlink is capable of is a tiny fraction of what fiber can do. It's better than having nothing. But it's not a replacement.

Starlink isn't resistant to attack either. It's in space. Anyone with launch capabilities can just launch a bunch of sand or ball bearings into those orbits and wait for the collisions to destroy the Starlink network. If someone does that, the only solution is to wait a few months to years for the mess to deorbit and try again.

Civilization is fragile. That's just the ugly reality of it. The solution is to kill the psychos trying to destroy civilization.