"whether made compulsory in law or through social pressure, it is doubtful that high voter turnout as such is a good indication of an electorate's capability for intelligent social choice." Encyclopaedia Britannica¹

"It is not compulsory in any other Western country - not the US or Canada or Britain or, across the ditch, in New Zealand. Why are adult Australians treated like children?" Derryn Hinch, Melbourne Broadcaster²

“In Australia, with compulsory voting, elections are won or lost often on the most irrational of reasons.”- Olympian Ron Clarke, head of the Council of the Encouragement of Philanthropy in Australia.³

In a nutshell

Despite Australia having a history of leading the world in electoral reform, it now is one of the exceedingly few democracies that still entertains the highly questionable practice of compulsory voting. Defenders of the practice claim that: voting is a duty; only a full vote gives the correct picture; in fact no one is actually forced to vote; and there is needed a protection from the dominance of extremist parties who can always get out the vote. However there are many who claim these defences don’t stand up to careful analysis and that the reason the major parties maintain this mandatory practice is of a less than noble motivation.  

Compulsory Voting – the Lifeboat Analogy

You are one of twenty two people who are stranded on a life boat after the pleasure cruiser sinks.

Yes there is enough room and supplies for all of you for the immediate future so no decision has to be made as to who will be thrown overboard.
However there is one problem: the skipper / navigator has gone down with the ship and no one actually knows which direction to row to ultimately reach the shipping lanes.
Even though no one knows for sure, eleven members of those on board have formulated ideas. Some think they can operate the sextant which has been saved, some believe they can tell which way to go by the currents, some by the sun, and some by the prevailing winds. The problem is that there is no general consensus from all these theories, and existing provisions will only allow for one attempt.
It is ultimately decided that a vote has to be taken to decide whose theory will be accepted to decide the course to follow.   Because the decision may well result in the life or death of everyone on board it is decided that everyone will have the right to vote.
Even though you yourself have come to no theory, you decide to vote with one person who, to you, gives the general impression of being  slightly more astute and knowledgeable than the other amateur navigators.
This leaves the remaining ten occupants. Not only do they have no idea which is the best direction for rescue, they also share equal faith in all of those who have suggested theories. Therefore because they fear their vote may lead to the wrong decision, they have decided to abstain from voting.

Will you allow the ten to abstain form voting or will you insist that, because lives are at risk, they  must partake in the vote?

Who profits from compulsory Voting?

In Australia the two major political parties/ coalitions have always supported compulsory voting.  Considering even those parties themselves admit that they would lose seats with voluntary voting, it is hard not to identify self interest in their advocacy of the current system.
Interestingly not only do they profit electorally, but as Peter Whelan, the erstwhile president of a small Australian political party the LDP suggests, they also profit in the word’s original meaning, financially.

 
… the discussion about non-compulsory voting should also cover electoral funding, as the two are closely  linked and are rorted by the major parties on both sides.
Currently any party which receives more than 4% of the primary vote, in any seat, gains electoral (read taxpayers’) funding of $2.24 per vote!
So after each general election, the winning party gets a huge windfall, but so too does the loser. After the 2010 election, Labor received in excess of $23 million. Even the Coalition got about $21million and they lost the election (exact figures are available on Australian Electoral Commission web site).
The rorting then becomes a “double dip” when a by-election is held. That was the case after the 2007 election, when in the next few months several Liberal/National Party sitting members resigned from safe seats, so their parties collected another round of electoral funding.
That huge windfall in funding then helps the major parties fund their future election campaigns!
The Coles / Woolworths duopoly pales into insignificance compared with the forced voting / electoral funding cash cow.
 

1 ‘Compulsory Voting’ Encyclopaedia Britannica 2001 edition.
2 Derryn Hinch, The Sunday Herald Sun, October 9, 2005.
3 Melbourne Herald Sun November 29 2002.