Unfortunately there are a few myths and inaccuracies in the preceding answers.
However, the
CAHS & Airways Museum website is indeed a good place to start for information about the history of Australia's airways system.
To understand why there were two branches of ATS with members in two different unions (or professional associations, depending on your point of view I suppose), one needs to understand how the airways system began and evolved. The result was simply a product of different pathways and operational responsibilities. For example, the first Aeradio Operators were not only communicators but also radio technicians. Whereas the first Air Traffic Controllers (as we would call them today) didn't use radio at all.
By the way, it's a common misconception that the
Kyeema accident was the origin of ATC. The real origin was a spate of ground and mid-air collisions at and near the major capital-city aerodromes.
Kyeema ushered in Flight Checking, later to become Ops Control (and now the responsibility of the aircraft operator).
Traffic_Is_Er_Was is broadly correct in saying that the early 'ATCs' were all senior pilots, some of whom just wanted a ground job and some of whom lost their flying medical. Norm Rodoni is a case in point, being the former Chief Pilot of Adastra Airways before he lost his medical and entered ATC. After the war there was an influx of ex-aircrew including the likes of Don Charlwood, a former bomber navigator. It wasn't until quite some time later that the first non-aircrew trainees were taken on (not sure exactly when, but possibly the early to mid-1960s).
The functions of both groups evolved over time until they had much in common, while still retaining distinctly different responsibilities, until moves began toward the integration of Flight Service and ATC in the early 1990s (completed in 2000). Many former FSOs re-trained as ATCs. I wouldn't argue to bring back the two separate branches of ATS, but one might question whether you really need the same highly skilled (and paid) traffic separator to also be doing 'traffic is...'. (This is not to denigrate the skills or dedication of the FSO, however.)
As for the Grand Canyon accident, there are many things that can be said about this accident from our lofty vantage point of 60 years on, not the least being the government penny-pinching that left the US airways system struggling to find ways to manage the burgeoning post-war civil air transport boom at a time when the Australian airways system, by contrast, separated all RPT aircraft. If you want to read a good, popular account of this accident, then I refer you to Mac Job's excellent
Air Disaster Vol. 4.