I can't believe this debate is still going.
Years ago, Boyd Munro did an excellent job of raising this issue. He then published a paper on monitoring 121.5. It was on the remnants of the air safety foundation for a long time, but the thread he started on pprune is still here:
http://www.pprune.org/pacific-genera...australia.html
As for the guys that think ATC will hear you on area frequency or that ADS-B will have your position, all I can say is I want some of whatever you are on.
When you've declared an emergency on area frequency in the circuit at Bourke you can come back and talk to me.
Anytime you have a second radio doing nothing, it should be on 121.5. What earthly reason other than laziness would you have for not doing this?