Ever since Bob Kiss of the Progressive Party of Vermont was elected mayor under the instant-runoff system, there has been a growing buzz about Instant Runoff Voting.
Many Kossacks support instant runoff voting because it seems that it would allow progressive candidates who are not Democrats to win, because they believe it eliminates the spoiler factor which has affected three of the last four Presidential elections, as well as the 1968 and 1912 elections.
Now, in areas where John Kerry got well over 2/3 of the vote like in Burlington, it will probably have that effect (although even in that election there was a minor overlooked problem). But what would be the likely effects of implementing it, say, statewide (no state voted for John Kerry by that much). Read below to find out.
The problem that affected even the generally successful Burlington mayoral election was that about 1/3 of the candidates who voted for a candidate other than the Progressive and the Democrat (Republican or one of the Independents) did not fully rank their ballots (see the exhausted pile in the link to the second round of voting in Burlington.
Given the fact that most states would be unwilling to spend the money necessary to explain the new voting system to the public, we can expect a far large percentage of ballots not to be ranked fully in a statewide IRV system. Although these ballots would still be counted, if those people's first-choice candidate was eliminated early, they would have no say in the final round. However, this issue is relatively minor compared to my other two concerns. The most major one is ...
The Spoiler Effect in Instant Runoff Voting
The one thing people who support instant runoff voting as a way to elect members of the Green party (in a race between the Green party, the Democratic party, and the Republican party) is that people choosing the Democratic candidate as a first choice will NOT always choose the Green party candidate as their second choice
A relatively significant minority of people who tend to vote Democratic are moderate in their political standings, and many of these people would probably choose the Republican as their second choice. This could lead to the following scenario (this is a plausible but of made-up scenario).
In this scenario, most of the people voting Green in the first round would be liberals who currently vote Democratic. They vote Green under Instant Runoff Voting because the Green is closer to their views and they believe the Green won't be a spoiler under IRV.
Round 1
Green: 45,000
Democrat: 35,000
Republican: 70,000
Notice that the sum of the votes for the Green and the Democratic candidates is 80,000. It's likely that nearly all those who voted Green as their first choice in this scenario would've voted for the Democrat if it was a plurality election. Therefore, in a plurality system, the Democratic candidate would have won the seat.
Let's assume that 80% of those who chose the Democrat as their choice chose the Green as their second choice, and that 20% chose the Republican as their second choice (in many cases the Republican would probably get more than 20% of the original vote). In that case, this would be the final result.
Round 1 Round 2
Green: 45,000(+28,000) 73,000
Democrat: 35,000(-35,000) ELIMINATED
Republican: 70,000(+7,000) 77,000
The Republican candidate ends up winning despite the fact that the majority of the voters would have preferred the Democratic candidate, and despite the fact that they were probably the last choice of over 45% of the electorate.
The effect of IRV on the Libertarian party
The Libertarian is by far the best organized third party in the country, and it is likely that they would win some seats currently held by both Democrats and Republicans (in relatively equal numbers), and would probably win more seats than the Green party.
The reason this would be bad is that the Libertarian party generally wants to virtually eliminate the government (pretty much pure capitalism with almost no regulations, making our current unacceptable division between the rich and the poor infinitely worse), and are even more against the environment than the Republicans are. Again, this second reason is much less important than the fact that the spoiler effect may well be exacerbated with IRV.