Your tone implies to me that you are under the impression that I'm suggesting one should not test their software. Nothing could be further from the truth.

What I'm saying is that it's foolish not to take any measures at runtime to validate that the system is behaving correctly.

Who's to say that the logs themselves are even formatted correctly? Your software could be perfectly bug-free and you'd still have problems without knowing it, due to bugs in some other person's software. That's the point you're missing - no matter how many edge cases you account for, there's always another edge case.