This argument seems interminable and there appear to be just as many arguments for one side as the other. It all seems to hinge around whether alerted see and avoid is better than unalerted see and avoid. My last near death experience was on a CTAF while on descent to the local uncontrolled airport, below CTA steps with an opposite direction Cessna. At no stage do I recall ever hearing from the Cessna on the CTAF. So alerted see and avoid does not work but the big sky theory did; the moving finger of fate did not write about our death that day. (By the way I was nearly cleaned up by a truck driving home and I have no idea which frequency the driver was on)
If we are trying to solve a problem, what is it? According to the ATSB Review of Mid-Air Collisions 1961-2003 <https://www.atsb.gov.au/media/36828/Review_of_midair_col.pdf> there were 37 collisions which means Australia averages approximately one per year. Of these 41% were near the five capital city GA airports, there were no dominant factors, and the figures are consistent with mid-airs in other countries.
So are we helping to prevent the remaining 59% of collisions by forcing pilots that have radios to listen on a specific frequency? The evidence would seem to indicate not; the 41% were probably on the GA airport Tower frequency receiving an ATS service.
A conclusion (not the only one) that can be reached is that it seems not to matter which frequency the pilots are on; what does matter is that they are looking out of the cockpit in every direction they can. Much in the way I drive my car or steer my boat. The air radio is very useful for getting assistance and making traffic calls but the report referenced above does not seem to indicate that it can prevent mid-air collisions. Short of having Class A airspace down to ground level, only concentration, eye balls and quick reactions can do that.
The latest threat to my life seem to be drones and I don't see CASA mandated which frequency they will be talking on!