Dick, it depends on how you quantify risk.
The premis of your argument in the first post is that 4 engines are safer than 2 and as a consequence casa are not meeting their obligations under the act by not putting safety first.
The basis of this premis is that 4 engines are safer than 2 - is that a fair summation?
I could mount an argument that says the risk of engine fire in a 4 engine aircraft is significantly greater than it is in a twin. It stands to reason that the risk of fire is worthy of consideration and is a significant risk given that the potentially burning engine is located in an area where a fire induced structural failure would be catastrophic. Add to that the fact that the burning engine is directly underneath a fuel tank and the potential is there for the world to come apart. Additionally extra engines increases the risk of an engine failure. It stands to reason that the more engines you have the greater chance you have of one of them giving up the ghost at an inopportune time.
On the basis that most aeroplanes have two or three hydraulic systems, a bunch of electrical systems, a pressurisation system and a couple of redundant controllers, and mostly replicated and redundant systems, regardless of whether they have 2, 3 or 4 engines, there is a strong case that says the more engines you have the riskier it is, so casa may well not be complying with their safety first obligations by banning etops and mandating 4 engine aircraft.
So how is your question answered? Well with the use of probabilities and risk assessments that determine that, on balance, the risk is acceptable given a number of mitigators are in place - these mitigators being the rules around etops/edto.
As for your mate -well he is a dill.
Does he advocate the use of a man with a flag to walk in front of motor vehicles or fit passengers with parachutes or simply ban air travel in its entirety as that would be the safest course of action and without doubt meet CASA’s obligations under the act.