Amongst the post-election entrail reading, I’ve seen a couple of people suggest that one of the reasons labour lost was due to a lack of tactical voting by Greens. If only Green supporters had held their nose and voted tactically in Auckland Central, Christchurch Central, Ohariu, and other close electorate races, the left would be better off.
These people do not understand MMP.
In MMP, there is one vote that matters: your party vote. Unless you live in Epsom, Oahriu, Te Tai Tokerau or Waiariki (electorates where strong candidates from minor parties could have brought in more MPs), your electorate vote is irrelevant to the outcome. All it does is select who your local representative is. But because the overall distribution of seats in Parliament is set by the party vote, it doesn’t change the final numbers unless there’s an overhang.
And to use some specific examples: Green voters voting tactically for Jacinda Ardern in Auckland Central or Clayton Cosgrove in Waimakariri wouldn’t have changed anything. These MPs would simply have become electorate MPs rather than list ones. Green voters voting tactically for Labour candidates in Ohariu or Christchurch Central would simply have traded Virginia Anderson or Tony Milne for Andrew Little or Sue Moroney (the last two people elected on Labour’s list). In Ohariu, it would also have got rid of Peter Dunne, but as he’s not bringing any extra MPs in, that’s really just a question of how much you dislike him.
Basically, under MMP, unless you live in one of a handful of seats, electorates don’t matter to the outcome, so you might as well vote for whichever candidate you like best.
What electorates do matter for is the prestige, survival and political careers of individual electorate candidates. And in the case of Labour, with a mix of electorate and list MPs and a strong FPP heritage, this causes misaligned incentives. The party wants party votes, but candidates – and especially candidates who have a low list ranking, or who have refused to go on the list – want your candidate vote. And so Labour had the joy of seeing a bunch of its electorate candidates put themselves first and run electorate-only campaigns, while letting the party vote wither. Their “success” in holding or taking electorates made no difference to the outcome, but did cost their party new blood (and the ability to get it through mid-term retirements) through the list. In some cases, it would have been better for the party if those candidates had lost, because while their list replacements are mediocre, they could at least have been forced out to make way for the new blood the party desperately needs.