David Cameron's speech against electoral reform performed a valuable service by highlighting how weak the arguments against AV (and for FPTP) are. Here's my point-by-point rebuttal.
1. AV is disproportional
The evidence shows that AV would have produced even larger Labour landslides between 1997 and 2005 . . . and larger Conservative ones in the 1980s.
Cameron is right. In a landslide situation, such as 1983 or 1997, AV does increase the winning party's majority as second-preference votes tend to follow first-preference votes. A fully proportional system is more desirable. But this is not as strong an argument against AV as some opponents suggest.
The system is designed to ensure that the government elected has the broad support of the majority of the population. Labour would have won more seats in 1997, 2001 and 2005, as Lib Dem voters preferred them to the Tories. Unlike under first-past-the-post (FPTP), it is not possible for a government with minority support to win a large majority.
In any case, the logical conclusion of Cameron's argument is to support proportional representation, not FPTP.
2. AV is too complex
I don't think we should replace a system that everyone gets with one that's only understood by a handful of elites.
How stupid does he think the electorate is? The fact is, millions of people already use the system. AV is commonly used for internal elections in businesses and trade unions, for most student union elections, for many American mayoral and district elections, and for Labour and Lib Dem leadership elections. In practice, no one has ever complained that the system is too complex.
3. AV means that some people get two votes
[I]f you vote for a fringe party [that] gets knocked out, your other preferences will be counted. In other words, you get another bite of the cherry.
What's wrong with taking second preferences into account? Cameron uses the example of the "BNP or Monster Raving Loony Party" voter who gets "another bite of the cherry". But what about the Tory supporter who wants to vote for their party in a Labour-Lib Dem marginal? Under AV, they can vote for the Conservatives without fear of enabling a Labour victory (by putting the Lib Dems as their second preference). But FPTP means they must either take this risk or hold their nose and vote for the lesser evil. AV would dramatically reduce the need for the depressing act of tactical voting.
4. Only three countries use it
Only three countries use AV for national elections: Fiji, Australia and Papua New Guinea.
But this fact has no bearing on the intrinsic value of the system. As John Rentoul has argued, this is "akin to saying that we shouldn't have an NHS because other countries don't".
5. AV means more hung parliaments
Hung parliaments could become commonplace.
Having complained that AV will lead to more disproportional outcomes, Cameron now warns that it will lead to more hung parliaments. He can't have it both ways. But that glaring inconsistency aside, he's wrong about hung parliaments. Australia uses AV and has returned one hung parliament in 38 elections. Conversely, FPTP in Britain delivered hung parliaments last year, in 1974, in 1923 and 1929 and twice in 1910.
Ultimately, whether or not AV results in a hung parliament (or a one-party majority of 200+) depends on the will of the voters. It's called democracy. Is Cameron opposed to this?