The problem with this line of thought, IMHO, is that you would then be advocating a safety net..followed by a 2nd safety net for the safety net..etc.
How about if there is a 5ft barrier and then a 10 foot safety net and a crazy/stupid parent THROWS the child over the net? Are you then going to say that they should have had a 30 foot safety net? You can ALWAYS find a way around ANY safety precaution. In the courts you have to prove willful neglect..The zoo has 2-3 safety precautions in place.. the mother places her child OVER/ON TOP of a safety wall and then DROPS the child. How in the WORLD can you say the zoo is even PARTIALLY at fault..The point of a safety barrier is to provide an extra layer of precaution..not to cure stupidity Last I saw they don't even know if the child died from the mother dropping him or from the animals.
This is truly mind boggling.. It's called the common sense rule. If you are standing in the middle of a road and get hit by a car, do you then say that the car should have a safety measure to gently move you out of the way prior to impact? It's not like the lap restraint failed..the mother failed her child.