> Those extra homicides "didn't happen", but the improvement is understood.

People are gonna criticize by saying "see? it was an overreaction to the problem, since there's not been many homicides at all!", when in fact the homicides were prevented by fixing the original problem. Same way with the electrician: "how much are you gonna charge again? And you're charging for a fix to a problem that didn't happen yet? Nah, I'll call you when the problem happens".

Its maddening.

> An electrician doing an inspection and noticing and fixing big electrical issues in the installation, would be appreciated, even if the accidents didn't happen.

Not if nobody knew he'd fixed it.