By pouring vitriol on an ally, the government only fuels confusion and cynicism.
SUDDENLY Labor, or at least many in it, have decided they must burn the Green witch. Prominent players have been stoking the fire all week, tossing the vitriol like kindling onto the pyre.
In most cases a Labor-Green mutual exchange of preferences in the Senate will be to both parties' advantage.
It's easy to understand why Labor figures see the need to mark themselves out from the Greens, and the reasons for their anger with their alliance partner. The Greens' refusal to compromise over asylum seeker policy has triggered an outpouring of frustration about the wider relationship.
The ferocity of the attack is something else. It's confusing to the public, another example of the ALP not getting its message out in a way that people can readily understand. Does Labor really want voters to draw the conclusion that the ABC's Annabel Crabb reached: ''If the government is really so convinced the Greens are loopy … then it should tear up its agreement''? Of course not. It wants people to simultaneously accept that the Greens are mad and bad, but that it's necessary and sensible to be bound to them by a formal agreement.
The Greens are trading off their victim status. In an email to their 60,000 supporters list that appeals for donations, leader Christine Milne says it is ''no coincidence'' that Labor's aggressive tactics have ramped up just before the byelection in the seat of Melbourne where the Green candidate is ''on track to win''.
The desperation of the hung parliament produced the formal Labor-Green alliance. There is some question as to why it was needed, given the Greens were never going to back Tony Abbott. But having them formally locked in was attractive to the embattled Julia Gillard, even if the subsequent dance was always going to be dicey.
The price of alliance was that the PM had to act quickly on carbon - which caused Gillard to break her pledge of ''no carbon tax''. It is intriguing to contemplate how things would have played out if Gillard had not made an agreement with them, and had stuck by her promise for long consultations on carbon pricing. She might now have more public trust; she wouldn't be defending a carbon tax.
If he'd been around, former finance minister Lindsay Tanner, who retired at the election, might have warned of the danger of entanglement. Tanner, who held Melbourne (now occupied by Greens deputy leader Adam Bandt), saw the juggernaut coming - in his seat, in the state seats in the area, and more generally.
In 2010 Tanner wrote that the Greens ''are harvesting growing support from a particular demographic that first emerged as a key part of Labor's support base in the late 1960s''.
The rising Green vote was a product of increasing tertiary education, he said, with their support concentrated among ''tertiary disciplines that are focused on much more than just making money''.
''Unlike most Australians, these voters tend to be secure and comfortable enough to be able to put aside immediate self-interest when assessing their political options. Unfortunately for Labor, their viewpoint is increasingly at odds with the perspective of Labor voters who aren't tertiary educated. On issues like asylum seekers, gay marriage, forests and civil liberties, such differences can often be stark. It's these differences that the Greens seek to exploit.''
While Gillard herself had some sharp words about the Greens in a speech last year, given the alliance and their sole balance-of-power position in the Senate, Labor previously hasn't been inclined to have a robust face-off. Indeed, for a long time it was notably understanding about the Greens' refusal to consider offshore asylum seeker processing.
Last week, things changed. Government whip Joel Fitzgibbon lashed the Greens in an opinion article about the asylum impasse: ''Labor's best chance is to call their actions for what they are and to tackle them head on.'' This was followed by New South Wales Labor secretary Sam Dastyari denouncing the Greens as ''extremists not unlike One Nation'' and foreshadowing he will move a motion at this weekend's ALP state conference calling on Labor to ''no longer provide the Greens party automatic preferential treatment in any future preferential negotiations''.
The motion also says that ''extreme elements'' of the Greens economic and social agenda are at odds with ''the values and needs of many Labor voters''.
Some Labor sources claim Dastyari's timing was driven by a desire to divert attention from controversial party reforms that he has been pushing, notably having the party membership elect state Labor leaders.
Maybe he just thought the time had come to take a stand and doing it around preferences underlined the point.
At one level, the preference stance is odd. The ALP can preference against the Greens now - there is not a binding party position saying it can't. And wouldn't it be expected to just act in its own interests?
The ins and outs of preferences can be hellishly complicated but in most cases a Labor-Green mutual exchange of preferences in the Senate will be to both parties' advantage.
The thought that Labor would preference against the Greens if that was likely to help produce an Abbott-leaning Senate seems ridiculous. In the lower house, while Labor preferences are not likely to be of much use to the Greens, the (small) difference between the Greens favouring Labor or running an open ticket can be important to the ALP in a close result.
On one interpretation, Labor's talk about preferences is partly designed to pressure the conservatives to preference against the Greens, as happened (to the Greens' great disadvantage) in the Victorian election. This might see off Adam Bandt (but no guarantee), and would help protect the NSW seats of ministers Anthony Albanese and Tanya Plibersek, which could be under threat from the Greens. The NSW Nationals are already headed to preferencing against the Greens everywhere. Tony Abbott has so far been evasive on the issue.
What Gillard thinks about the great Greens debate is unclear. When asked about preferences she has said it's a matter for the organisation (which forgets former leader Kim Beazley's strong declarations about putting One Nation last).
While it is undoubtedly necessary for Labor to separate its ''brand'' from that of the Greens, this should have been the approach right from the start of the minority government, even at the cost of sometimes making Labor-Green relations testier. Given that it is being done now, however, a more subtle approach was necessary. If you throw insults of ''extremism'' and ''loopy'' at people after giving voters the impression that they are your friends, you can't blame the electors if they are cynical.
Michelle Grattan is political editor.