A point that should be remembered is that the class of material the Australian government currently seeks to block with a mandatory ISP-level filter is far broader than any other Western democracy attempts to block with voluntary ISP-level filters and that it was once broader still.
Until the Government recently narrowed the target of its policy to just RC-rated content, the Government had been intending to block all 'prohibited online content' and 'potentially prohibited online content'. This category included X-18+ material and R-18+ and MA-15+ rated material not subject to age-verification mechanisms.
For a detailed analysis of what the Refused Classification category includes, please see Irene Graham's libertus.net