From a recent Michael Kirby speech [pdf]:
For example, our Constitution is too rigid. It is one of the most difficult in the world to amend. This feature of Australian legal arrangements can sometimes protect us from the risk of mistakes, as in the Communism referendum of 1951. But the rigidity also helps produce a national constitutional lethargy that despairs of needed alterations and of fresh thinking about our basic governance.
This doesn’t survive empirical scrutiny.
This is a bar graph of the referendums and the % of states voting for it, as well as the percent of population. A larger version of this graph can also be viewed.
For an Australian referendum to pass it requires an absolute majority in both houses of parliament, a majority of electors and a majority of states. The Communist referendum that Kirby mentioned did not get a majority of electors (49.44%) or states (50%), so would not have passed under a system that only required a majority of electors. Menzies illiberalism was not saved by the constitution in this instance.
A few referendums got more than 50% of the elector’s vote but not a majority of states, such as three of the 1946 referendums on social services, marketing and industrial employment; but this was after having been rejected constantly in prior referendums.
With Australia having a small number of states this makes any alteration of the constitution require a massive majority, and those that have passed, have done so overwhelmingly. For instance the retirement of judges passed in all states and with 80% of the electors vote.
In reality though, we can say that the requirement for the majority of states is not necessary. The outcomes are pretty much the same. I suspect it was introduced as part of the ‘federal’ character of the system, where the majority of electors was the ‘national’ character of the system – but either way it does not make enough of a difference to warrant its inclusion.
So why is the Australian Constitution difficult to change?
It isn’t really, but then, why have so many referendums failed? The problem is the quality of the referendums. If you categorise them into Democracy, Centralisation (increasing the power of Canberra), Illiberalism and Other (Republic and preamble), then you get a graph like this:
Notice the overwhelming number of referendums to centralise and how few passed. Voters have been rejecting centralisation. Most of the referendums to increase the power of the national government stopped in 1948, by this time the federal government was able to expand their power without the need to go to referendum.
This was mainly through having the power of income tax, which was gained in the emergency of WWII, and the increasingly national-minded, as opposed to federal-minded, High Court which has been a supporter of centralisation. A good example is Workchoices. There have been three failed referendums to gain Industrial Relations as a National Government responsibility. Workchoices achieved that power without having to go to referendum through a High Court decision.