Key points
- A shift from first-past-the-post to PR shifts party competition from being within parties to being between parties. It is not clear that this is good.
- Under PR you get more parties. This includes far right parties. There is a significant advantage in future electoral competition once you've become an established party.
- Coalitions have the problem of it being hard for voters to hold specific parties or leaders to account for policies.
- Coalitions create a free rider problem because the reputation of the coalition government is a public good.
- The median voter theorem no longer holds. If voters have extremist tendencies there is no competitive pressure not to serve them
- Italian and French politics look not good. Having non FPTP seems plausible to have played a part in this in that it allowed Front National to gain a significant foothold in France while no equivalent far right party has sprung up in the UK. The Northern League is not fascist but is hard right and is currently the largest party in the Italian Parliament. The Brothers of Italy are literally neo-fascists and have been part of Italian coalition government and plausibly could be again.
- Big tent Social democrats competing with Christian Democrats seemed to work fine.
My claim isn't that first past the post is clearly better than other electoral systems, but it's not clearly much worse and so I wouldn't expect it to pass the very high bar of being an EA cause area.
An important point note is that these arguments apply much less strongly to the US because of the much weaker parties.
I may or may not write a more detailed account of this, but given my record of trying and failing to write good forum posts, this may the best I'll do.
Coming back to this thread now having thought about it more. Speaking from my personal experience as an American citizen, I think the spoiler effect lowers voters' confidence in the electoral system, especially that of idealistic, young voters.
I was a Bernie supporter in 2016. I wasn't excited about Hillary being the Democratic nominee, but because I understood the incentive structure created by FPTP, I chose to support Hillary in the general election because I really hated Trump. But, there was a substantial number of Bernie supporters who defected from the Democratic base after Bernie lost. Mainstream Democrats seemed to be shaming them into voting for Hillary, on the grounds that:
This has been called vote-shaming, and I think it makes American political culture a lot more toxic because it pits ideologically similar people (like center-left and far-left progressives) against each other. Many people don't vote at all, both because of voter suppression, and because they don't feel represented by the major candidates. Eligible non-voters in 2016 were also more likely to be younger, less educated, less affluent, and non-White (source), which suggests that the system is not representing these groups as well as it could be. It is a problem that citizens of the world's oldest continuously running democracy feel disempowered - it means that the government is not as responsive to citizens' interests as it should be. Vote-shaming puts the blame on individuals for not voting, instead of the system for causing vote-splitting.
Just so you all don't think that this only happens on the left: I have a friend who didn't really like either major candidate. He leans conservative and strikes me as someone who might have preferred the Libertarian Party or Bernie Sanders. Despite not liking Trump that much, he voted for Trump in the 2016 general, because he thought Hillary was worse.
Some statistics:
I think that increasing voter turnout would make the government more responsive to citizens' interests, and I think changing the voting system we use would help with this because it would help citizens feel more empowered to vote.
Note: I'm not saying that vote-splitting, or even problems with the voting mechanism in general, is the only issue with the U.S. electoral system. I think there could be other problems introduced by a new voting system such as approval voting - practical problems that degrade the political system similarly to the way that I think vote-splitting does (since we know that no voting system is theoretically perfect).