"One mistake can cause a breach" and "we should fire people who make the one mistake" are very different claims. The latter claim was not made.

As with plane crashes and surgical complications, we should take an approach of learning from the mistake, and putting things in place to prevent/mitigate it in the future.

I believe the thread starts with cybersecurity as a job role, although perhaps I misunderstood. In either case, I agree with your learning-based approach. Blameless postmortem and related techniques are really valuable here.