Sigh... The real world doesn't work that way. It's really that simple. As long as there is a human element involved there is room for mistakes, for incompetence, for that one guy that was supposed to check the other guy's work but didn't because it's been a long day and he's tired and his partner always got it right before, or they've never worked together, or he's a rookie, or...whatever. I get what you're saying, but I suspect that you haven't worked in a field that has grave consequences for mistakes. Through training and discipline you're able to minimize risk factors, but at some point the stars align and something you didn't anticipate happens. Look at Corrections and early parole. The PO reviews the case, makes a decision to release to the community, the parole board reviews that, approves, and out the con goes. How many times have we all hard about recidivism (in some cases really nasty stuff) where someone re-offends and ends right back in the slam?
Regulation helps, but enforcement has to come through audits and response. The 1st is usually random and the 2nd is after the fact. How does that stop the Boogyman from showing up?