Who says it’s defeatist? It’s realism. You might as well say noting mild steel only has a 60-80kpsi yield strength ‘defeatist’.
That attitude allows practical risk management and effective engineering. Pretending software can be secure or mild steel has infinite yield strength cannot.
There is no lock that can’t be picked either, which is why no one leaves millions in cash protected just by a lock without guards and a surveillance system. And why they insure large amounts of cash.
At this point it should be pretty obvious - don’t put important secrets on computers without a way to expire/revoke them. If it’s a secret that can’t be expired/revoked, think long and hard about if you need it on a computer - and if you do, use a SCIF.
Monitor any connected computer systems for compromise. Use encryption extensively, preferably with hardware protection, because software is insecure, etc.
Same with controlling dangerous equipment - don’t rely on pure software or someone will get killed. Use hardware interlocks. Use multiple systems with cross checking. Don’t connect it to the internet. Etc.
This is all industry best practice for decades now.