I don't think it's necessary to physically cut cables.
What if critical infrastructure is isolated from savages by just not having routes to/from them?
I mean, in a similar way the Team Cymru UTRS[1] works by publishing a list of BGP filters to be imported in routers.
Agreed, it was a metaphor and not really meant as a call for physical damage that would (presumably) later have to be fixed again anyway. I should have written that more clearly.
[1] https://team-cymru.com/community-services/utrs/