"The banks could have bought insurance against rising interest rates, but they didn't. "

See, this always worried me. How do you buy insurance against rising interest rates? Or more precisely, WHERE to you buy insurance against rising rates? If the answer is "from other banks" (which it presumably is), then there is no hedge in any meaningful sense. My reasoning is that it's a closed-loop system. They can't all pay off each other without counterparty default somewhere along the line.

I guess what I'm trying to say that rising interest rates are bad in the sense that it creates losses (be they realised or unrealised) that are systemic to the whole banking system. There needs to be some outside party that can soak up the losses. That outside party is The Fed