Does compulsory voting limit our election choices?

It's the democratic scandal that few people notice.

In the upcoming election, thousands, perhaps millions of people will be legally prevented from voting the way they want to. Or to be precise, they'll be prevented from not voting the way they want to.

Australia is one of only 17 countries around the world that compels its citizens to go to the polls. Our fellow enforcers include a handful of developed democracies such as Belgium, Luxembourg and Chile, as well as some politically unstable countries like Congo and Thailand. What is quietly accepted as a fact of life in Australia is very peculiar by international standards.

The main argument you'll hear in favour of compulsory voting is that it's a basic civic responsibility that comes with living in a democracy.

I agree wholeheartedly. Anybody who can't be bothered walking down to their local primary school on one Saturday morning every three years can't complain if they get the government they deserve.

Expecting people to vote isn't much to ask. The AEC makes voting in Australia easier than virtually anywhere else in the world. If you can't get to the primary school your options include a postal ballot, voting anywhere else in your home state or voting ahead of time.

You can vote while overseas, in hospital, in a nursing home or even while you're in prison in some circumstances. There's really no excuse not to vote.

Well, except for one. You might just not want to.

With Australia's unique combination of compulsory voting and compulsory preferential voting, people in all but a tiny number of electorates are legally obliged to choose, in the end, between a Labor and Coalition candidate.

The only way to avoid having to do so without copping a fine is to deliberately cast an informal ballot.

In the 2010 election, 5.55% of House of Representatives votes were informal. Many of those would have been genuine errors by voters who were attempting to cast a formal vote. Included in that number, however, is a small number of citizens who are rejecting all of the available options.

By opting out, these people are making a legitimate political statement, and it should be heard loud and clear by the parties that are letting them down.

Most people, of course, end up casting formal ballots regardless of whether they would do so under optional voting. But political activist Albert Langer has proven the appeal of opting out.

In the 1980s and 1990s, Langer publicly advocated that people cast an equal preference for any candidates they chose not to support, allowing their votes to exhaust after all valid preferences had been distributed instead.

Langer's campaign led to changes to the Electoral Act banning such advocacy, a High Court challenge to the amendment and even landed him in jail for breaching a court injunction against distributing his material.

The publicity surrounding the Langer case saw a 500% increase in exhausted ballots at the 1996 election.

Clearly, the more that people knew they could vote without preferencing the major parties, the more they did so. The Electoral Act has since been amended again to make such votes informal.

Compulsory voting does mean that many people end up casting a ballot who might not otherwise do so. Australian voter turnout averages above 90%, far higher than comparable democracies with optional voting.

But it also distorts our political system and the policies that the major parties produce. With a captive audience of people who have to vote and ultimately send their preferences to one of two candidates, the major parties have an incentive to be as similar as possible to each other.

If you've ever complained that Labor and the Liberals seem to be the same, compulsory voting is a major reason why.

To explain why, I'm going to talk about economic theory for a moment. Forgive me. Hotelling's Law is a fairly simple observation that competitors, of any type, tend to be better off by being as similar as possible to each other.

Imagine two gelati trucks parked at a beach. The two trucks sell the same flavours and also have the same prices, since if one was more expensive than the other people would walk past it to go to the cheaper one.

The only difference between them is where they are located along the beach . Where do they park?

Because they offer the same products at the same prices, the only thing that should determine which truck customers go to is how far they have to walk. If you assume that people will always walk the shorter distance if possible, then the logical place for the two trucks to park is half-way along the beach, right next to each other.

If one truck were to instead park at the far northern end of the beach, then the other could move further to the north, capturing not only all the customers from the southern half of the beach but a fair chunk of the northern half as well.

The first truck would naturally respond by moving further north to win more customers, until both trucks are parked in the middle of the beach, where they are closest to 50% of beach goers.

Australian major parties, unlike those in optional voting countries, can be absolutely confident that any voter who at least dislikes them less than the other side will ultimately vote for them.

In the United States, the Democrats and Republicans spend a sizable portion of their time and money on appealing to their own supporters and convincing them to come out and vote.

Labor and the Coalition can instead treat the votes of the vast majority of Australians as safe for one or the other, and fight over the small percentage of swinging voters in the middle.

Kevin Rudd doesn't need to listen to Labor's left-wing on asylum seekers, because they're never going to vote for Tony Abbott anyway.

As much as they might not like the Papua New Guinea Solution, they like Abbott even less. They are a captive supporter base.

The result is two parties, like two gelati trucks at the beach, that are best off positioning themselves as close to each other as possible.

Whereas the Democrats and Republicans offer dramatically differing platforms to their respective bases, the differences between Labor and the Coalition tend to be much, much smaller.

They are still there, of course (Abbott promises to turn asylum seeker boats around, and Rudd doesn't), but if they become too great one or the other party will move left or right to take advantage of the gap.

Compulsory voting, by forcing us to make a choice even if we'd prefer not to make one, ends up leaving us with less choice than we would otherwise have.