Terrorism is just a label, the assessment is that if you take down a couple SV or Calf substations at a need for high production, the grid or a big chunk of it fails and can't be brought back up without replacement transformers that aren't there. If the avg electrical engineer agrees with that, then some expense to shield transformers are in order as well as production of replacement transformers to hold in inventory: locate them regionally so they can be trucked to the site of a failure or attack and maintaining the grid in this context may be economically feasible.

Armored doors on cockpits -a debated topic prior to 911 that has lost the sense of being debatable since, every major jet has them now.