Pluralism, otherwise known as single member voting, first-past-the-post, majoritarian voting, or in Australia, the rather confusing designation of ‘preference voting’, is the electoral system whereby all the people living in a specific geographical area will end up being represented by just one candidate despite the fact they may well embrace quite divergent  political beliefs.
This winner-take-all approach still exists in the United States and Britain and most ‘old world’ democracies which have roots in the erstwhile British Empire, but has rarely been embraced by European countries or by modern nascent democracies that have risen in the last quarter century.

Problems

The Gerrymander

"Gerrymandering is one of the great political curses of our single-member district plurality system."
Professor Douglass Amy Real Choices, New Voices, Columbia University Press, 1993

“in U.S. politics, drawing the boundaries of electoral districts in a way that gives one party an unfair advantage over its rivals. The term is derived from the name of Governor Elbridge Gerry of Massachusetts, whose administration enacted a law in 1812 defining new state senatorial districts. The law consolidated the Federalist Party vote in a few districts and thus gave disproportionate representation to Democratic-Republicans. The outline of one of these districts was thought to resemble a salamander. A satirical cartoon by Elkanah Tisdale  appeared in the Boston Gazette; it graphically transformed the districts into a fabulous animal, “The Gerry-mander,” fixing the term in the popular imagination.”                  "gerrymandering." Encyclopaedia Britannica 2008 Ultimate Reference Suite

In the above table, representing an election of just five districts, it can be seen that the Labour Party has won owing to winning the majority of seats, despite the fact they gained fewer votes.
For a good gerrymander it is best to ensure that expected opposition seats are drawn to be as homogeneous as possible while electorates one hopes to win are drawn such that there will be a bare majority of supporters.

“[Reforming the electoral system towards proportional representation] is not a radical proposal. It is practical and reasonable. Most importantly it would ensure that a party with a minority of the two-party vote never accidentally ‘won’ an election again-as the Howard government did last October.  Howard enjoys a 12-seat majority in the House of Representatives having attracted only 48.7 per cent of the two-party preferred vote. If democracy can be defined as a situation wherein the will of the majority prevails, then Labor leader Kim Beazley should have formed government after the last election. Worse still, this outcome was not exceptional. In one in four Australian elections, the electoral system delivers government to the wrong party. It is worth noting that in other, less politically stable countries, similar outcomes have led to popular revolution.”

Extract from Representation and Institutional Change, ‘Papers on Parliament No. 34’,  December 1999, Department of the Senate, Canberra. pp116-117.

Pork Barrelling

Typically [pork barrelling] involves funding for government programs whose economic or service benefits are concentrated in a particular area but whose costs are spread among all taxpayers. Public works projects and agricultural subsidies are the most commonly cited examples, but they do not exhaust the possibilities. Pork barrel spending is often allocated through last-minute additions to appropriation bills. A politician who supplies his or her constituents with considerable funding is said to be "bringing home the bacon."   Wikipedia

Pork Barrelling is the practice of members of a country’s S.M.V. legislature gaining special benefits for their own particular electorate so as to keep them in good grace with their constituents. Although technically not a bribe, it does border on the unethical because even though it is the duty of politicians to care for the welfare of the public, there does seem little justification to arrange benefits for just one segment of the population at the obvious expense of all others.

Of course in theory it could also happen with proportional representation systems. Politicians will still have constituents whose vote they want at the next election even if they don’t all live in the same area. However in practice it would be a lot more difficult pass on a ‘gratuity’ to people when there is no pretext for giving it to them apart from the characteristic of the voters themselves.    What justification can you have for legislation that grants money to  people because they support environmental measures, or believe in capital punishment or believe that we should not be involved in foreign military entanglements?  

The chief executive AND your local member

One of the most bizarre aspects of pluralist voting when it is applied to responsible government systems, is the fact that someone as important as the prime minister also remains, because he or she is still a member of the lower house of parliament, the representative of the electorate from which he/she is based and is duty bound to be the one handling all local concerns.  It seems incongruous that someone who may well be involved in strategically important discussions with world leaders about their united involvement in theatres of war, might also have to talk a call from a constituent complaining that the aircraft noise from above his farm is stopping his hens from laying.

A party decapitated
The incongruity becomes even worse at election time. A party could either win or present a reasonable result at an election and yet be in the position of having its leader lose his own seat and thus not be able to join  his comrades in parliament. This extreme embarrassment happened for Australian then Prime Minister Stanley Bruce, who in the 1928 election, lost his own seat and had to wait three years before he could return to parliament.
Many are predicting a similar situation will happen in the upcoming 2007 Australian federal election. Prime Minister John Howard, who polls declare has the best chance of leading his Liberal Party to victory, is now fighting a tight race in his own electorate of Bennelong, due to a recent electorate boundary redistribution which removed some erstwhile supporters while added some voters with unknown loyalties.
Of the approximate twelve million voters in Australia, it would be fair to say that at least five million would prefer the Prime Minister to remain in office. However, because there is no guarantee that a needed majority of 40,001 of that 5,000,000 actually live in Bennelong, there is a very real possibility that the Liberal Party, even if it wins, could be without its leader in the new term^§.

The two-party system

A two-party system often develops spontaneously from the single-member district plurality voting system (SMDP), in which legislative seats are awarded to the candidate with a plurality of the total votes within his or her constituency, rather than apportioning seats to each party based on the total votes gained in the entire set of constituencies. This trend develops out of the inherent qualities of the SMDP system that discourage the development of third parties and reward the two major parties.                Duverger's law   Wikipedia

…in 1906 one of our founding fathers, our second prime minister Alfred Deakin, had done much to unite the warring anti-labour factions as a single political force. It may not be stretching things too far to say that our two-party system of parliamentary democracy arrived, fully packaged [in that period]…         Evan Williams*

It is hard to understand why the advent of a political system that limits the number of political parties to only two should in any way be celebrated. Should voters feel privileged that they have only two viable options at election time? Are we to assume that  so called third, or minority party supporters, are not concerned about the fact that they are destined to never achieve representation in SMV houses of parliament? 
Despite democracy-challenging ‘virtues’ of the system such as the fact that “Uncommon and unconventional ideas remain non-influential”, most comment on this duopoly practice tend to emphasise its disadvantages.
It is interesting to note that in recent years in Australia, where there has been the loosening of regulation of the media and the liberalising of its ownership laws, many major party politicians have complained about “the concentration of media ownership” with regards to its effect on free speech and democracy. This alleged concentration relates to, at the very least, six independently owned publishing entities, either radio, newspaper, periodic journals, television free-to-air or television subscription, and yet when the subject becomes democracy itself, these same politicians never seem to complain about the concentration of only two political parties that pluralist voting generally limits us to.

Australia

1998 

• In the federal election John Howard of the Liberal Party ran against the Labor Party’s Kim Beazley.
  Loser Kim Beazley received only 5,630,409 votes while the winner John Howard, owing to the gerrymander effect, lead his party to victory and government with the grand total of ... 5,413,431 indications of support from the Australian public.
• The average number of formal voters for each House of Representatives district in this election was 75,061. As only a majority of votes are needed to win, gaining on average 37,531 votes in any district would be all that is necessary to win that seat. Throughout the whole country Pauline Hanson’s One Nation party accrued twenty-five times that figure, 936,621 votes,  yet failed to win a single seat.

1990,  1969, 1961, and 1954

• As above, the winning party leaders and incumbent Prime Ministers, Bob Hawke, John Gorton and Sir Robert Menzies(twice), won fewer preferred^# votes than  the opposition of the day.

1980

• In the Northern Territory’s first election, held in October 1974 , the Country Liberal Party  gained  13,690 votes as against the party with the next highest number of votes, the Australian Labor Party with 8,508. The CLP won seventeen seats while the ALP won ......none.

United Kingdom

2005  Tony Blair’s Labour Party won power despite 64.8% of the voters not giving it their support. In just England, Labour won 286 seats despite gaining fewer votes than the Conservatives, who won only 194 seats.

1951  Despite gaining more votes, Prime Minister Clement Attlee was defeated at the national election by Winston Churchill.
1974  Despite gaining more votes, Prime Minister Edward Heath was defeated at the national election by Harold Wilson.

Canada

Fair Vote Canada presents this list of electoral low points in recent decades. Beginning with number eight they work their way down to number one.

THE LOWEST POINTS IN CANADIAN FEDERAL ELECTIONS 1980-2004

8. In 1984, the Progressive Conservatives win 50% of the votes but gain nearly 75% of the seats, close to an all-time record for the largest percentage of unearned seats in any federal election.

7. In 2004, more than 500,000 Green voters fail to elect a single MP anywhere, while fewer than 500,000 Liberal voters in Atlantic Canada alone elect 22 Liberal MPs.

6. In 2000, twenty-two candidates become MPs despite winning less than 40% of the votes in their ridings (electorates).

5. In 1993, the newly formed Bloc Quebecois comes in fourth in the popular vote, but forms the Official Opposition by gaining more seats than the second place Reform Party and third place Tories.

4. In 2000, 2.3 million Liberal voters in Ontario elect 100 Liberal MPs while the other 2.2 million Ontario voters elect only 3 MPs from other parties.

3. In 1993, more than two million votes for Kim Campbell's Progressive Conservatives translate into two seats – or one seat for every 1,000,000 votes. Meanwhile, the voting system gives the Liberal Party one seat for every 32,000 votes.

And finally, the two chart toppers…

2. In 1984, when competing for the Liberal leadership, Jean Chretien tells reporters in Brandon, Manitoba, he would introduce proportional representation "right after the next election" if he became prime minister.

1. In 1993, Jean Chretien wins the election and begins his ten-year reign as prime minister. In three elections, he never wins more than 42% of the popular vote, but still forms "majority" governments thanks to the current voting system. He never gets around to introducing proportional representation.

# With Australia’s preferential voting system for single member seats, ALL votes eventually end up with either of the two larger parties. This is because the voter must indicate on the ballot paper not only his primary choice but all preferences all the way down to his last choice. Thus in the so called ‘two party preferred’ final tally, votes from losing smaller parties will be distributed upwards towards the larger parties according to the actual preference on each individual ballot paper. 

§ Technically, allowance is made in the Australian Constitution for procedures to attempt to bring ‘a winning leader without seat’ back into office. Section 64 allows the Prime Minister (as a Minister of State) to remain in his position for three months without being a member of Parliament. This would be sufficient time to arrange for a junior member of his own party to resign his seat and allow the Prime Minister to contest the subsequent by election. However, this is not a perfect solution. It is offensive to the people of the electorate to tell them that the person they have recently given their approval to, has now resigned and that they must again go to the trouble of voting to choose a representative. While the whole cost is an added drain on the state coffers, the new candidate obviously has no roots in the local community and there is still no guarantee that he will win.

*Evan Williams, The Weekend Australian:  Review, Nov 10, 2007, p.9