One common criticism of proportional representation systems is that "they let in all the radicals." One more nuanced formulation is that they're structurally biased in favor of leftists.

James Q. Wilson in an essay for the American Enterprise Institute recently made one such pass at PR:

The system a country uses to elect its rulers also makes a difference. In a recent study, political scientists Torben Iversen and David Soskice have shown that, among seventeen large democracies, those that elect their legislators using proportional representation (PR) are three times more likely than those electing them by majority vote to have leftist governments that redistribute income from rich to poor.

Australia, Canada, Japan, Great Britain, and the United States have majoritarian systems, while Austria, Germany, Italy, and Sweden have PR systems. Under a PR system, several parties will compete, while in majoritarian systems, only two parties usually contest elections. If there are several parties, middle-class voters will support programs that tax the rich and benefit themselves, knowing that they can change their voting habits if a government wishes to tax them more. But if there are only two major parties, middle-class voters will worry that voting for leftist parties will mean more taxes for them, so they will be inclined to support right-wing parties.

Many leftists, of course, hold Sweden up as a beacon of social democracy. But recent election results from that country subvert the empirical point above. Despite seven effective parties and open-list PR, last weekend's election seated a center-right government. The coalition ran mainly on a platform of tax cuts.

Sept. 17 (Bloomberg) -- Sweden's opposition, headed by Fredrik Reinfeldt, ousted Prime Minister Goeran Persson's Social Democrats from power in the closest election in 27 years, after promising to cut taxes and boost employment.

The four-party Alliance for Sweden, led by Reinfeldt's Moderates, took 48.1 percent of the vote, compared with 46.1 percent for the Social Democrats and their allies, the Greens and the Left Party, according to a count of 99 percent of electoral districts by Sweden's Election Authority.

Reinfeldt successfully argued during the election campaign that the Social Democrats, who've been in power for 12 years, had failed to create jobs and promote new businesses. At the same time, he pledged to maintain the bulk of Swedish welfare programs, the fruit of the Social Democrats' domination of government for 61 of the past 70 years.