Secondly,I am not sure all those who loudly proclaim that there is no "scientific" way to prove one way or another that singles are okay, are not bottom line driven and pro-operator advocates.
The 'bottom line' drives all decisions whether they be regulatory, design, or operational. When something becomes expensive to purchase or operate, it use becomes limited or restricted. At some point anything can become cost prohibitive and use will be terminated. This is true even for governments.
How about risk? If it was proven that more engines were safer, would you fly in a twin when a four engine aircraft was available? Certainly 4 engines are better than two. How about six engines, or even eight! That would be even safer. Needless to say if you never flew at all, that would be the safest option. At what level is risk acceptable? If it could be proved scientifically that 95% of all accidents were caused by pilots with less than 25,000 hours, should all others with less time be restricted?
Would you want the JAA to impose a requirement that any helicopter flown at night or over a city must have eight engines and a crew of four (pilot, co-pilot, flight engineer, and navigator-all of whom at appropriate CRM training)? If one could scientifically prove the risk would be lower, how could you argue against such a requirement?
Finally, would any of these gentlemen(including members of the NTSB) send their families on a trip over the Amazon in a single engine airplane?
Anyone (including members of the NTSB) would send their families on a trip over the Amazon in a single engine airplane if the risk of that trip was less than the risk of some other option. Flying in a single engine would be safer than walking across the Amazon. It would be safer than attempting to drive or kayak or balloon across the Amazon. Would a twin be safer? Maybe. Would you fly in a old, poorly maintained twin rather than a new and superbly maintained single? Would you fly in a twin flown by a pilot with 200 hours and no nav instruments or would you prefer to fly in a single with two 20,000 hour pilots with sat nav and full flight director?
How about that bottom line. Would you take a trip in a twin that cost 5,000 euros when the same trip in a single cost only 50 euros? Thousands of people every day select low fare options over higher fares even when the are completely aware of the additional risks.
Like it or not, these are bottom line questions. Yes, they are also pro-operator because when nobody can afford to fly a helicopter because the cost to purchase an appropriate helicopter becomes to high, and the cost to operate that helicopter (landing fees, maintanence, insurance, registration costs) becomes to high, or the use of the helicopter becomes to restricted; then there will be no civil operators, owners or helicopter pilots.
Then there are the eco and ethical questions. Two engines, bigger carbon foot print. Two engines equals less operational aircraft which equals less people saved by EMS. If you were laying on the road, bleeding with life threatening injuries, would you refuse that night flight in a single because the risk was too high?