In exiting from Act and then Parliament in next to no time, David Garrett has done the right thing. Not that he had any choice. It was the only thing he could have done.

Still, the way he has handled his forced departure from politics has allowed him a modicum of dignity to alleviate the mountain of opprobrium under which he is now buried.

In contrast, past disgraced MPs, namely Taito Phillip Field and Donna Awatere Huata, brazened it out, clinging to their parliamentary seats - and thus their salaries and perks - long after the parties that put them there had gratefully, if belatedly wiped their hands of them.

The difference between Garrett and the latter is that Field and Awatere Huata still had to go before the courts. Garrett may have been discharged without conviction in a court of law.

But from the moment he revealed his theft of the identity of a child for fraudulent purposes, he was convicted in the court of public opinion, left devoid of any moral authority and disqualified from slipping into similar backbench purgatory, such was the heinous nature of his crime.

However, that Garrett technically could have carried on dining out on the taxpayer until the next election has irked many people. How could someone who was an MP by virtue of his slot on Act's list suddenly become an independent MP?

The short answer is that MPs have been able to leave their parties without sanction since the sunset clause in the Labour-Alliance coalition's anti-party-hopping law kicked in and the act's provisions expired. That was five years ago.

The absence of such a mechanism in the Electoral Act is seen as another black mark against MMP.

These are the best and worst of times for the country's mixed-member proportional voting system, whose future goes on the line in two forthcoming referendums, the first coinciding with next year's election.

The unity of purpose displayed by political parties after the Christchurch earthquake demonstrated an MMP-elected Parliament can respond rapidly and constructively to crisis.

It is difficult, however, to dispute the Prime Minister's assertion that Act's internal ructions will increase the likelihood of MMP getting the boot.

Act has followed the Alliance and New Zealand First in being torn asunder by the stresses of a governing arrangement. The Greens have avoided that now-familiar route to oblivion by simply not being offered it.

The Maori Party has so far coped with the inherent contradiction between the low socio-economic status of its voter base and its backing of a centre-right Government. But for how long?

It is not so much the tail wagging the dog that is turning voters off MMP. It is the tail dropping off the dog through incessant wagging just to get noticed.

As John Key also noted, disillusioned voters are shifting back to the two main parties. The combined Labour-National party vote increased from 62 per cent at the first MMP election in 1996 to nearly 80 per cent in 2008.

Even with the opportunity to split-vote, around 70 per cent of voters cast both votes for the same party.

The relative homogeneity of our society works against minor parties searching for niche votes. On top of that, the cautious and conservative electorate's antipathy to radical policies on either side of the political spectrum has Labour and National hogging the centre.

There is precious little room for anyone else. That has essentially been Act's problem and is the root cause of its current ructions.

There are simply too few voters residing at the point of the spectrum where Act would like to set up camp. So Act chased the populist law-and-order vote. And that is how it ended up with Garrett.

Despite National's seemingly blasé and detached view of Act's exercise in self-evisceration, the latter's problems have serious and worrying implications for National.

That is not because the Act caucus might collapse before the election. That is of minor concern to Key.

It is after the election that the turmoil within Act may really hit home for National when it finds itself without a compatible ally bringing even a handful of seats to the negotiating table in the manner the Greens will for Labour.

Of course, Tariana Turia and company may well happily climb back on board National's wagon. However, National's membership would bristle at being hostage to the Maori Party and the concessions that would entail.

National is increasingly pinning its hopes on securing an outright majority, something voters were unwilling to give Helen Clark when Labour was cresting 50 per cent in the polls in 2002.

All of this means the electoral referendums take on huge significance. A shift from the current true proportional electoral system to the token-proportional, effectively first-past-the-post supplementary-member system is starting to look like a lifeline for National.

Officially, National has not declared a preference for any particular outcome from the two referendums, the first of which will indicate whether change is favoured by the electorate and the preferred alternative.

The second - which will be held at the 2014 election if there is a majority for change in the 2011 ballot - will pit MMP against that alternative.

Key will tread carefully. His observation that Act had damaged MMP was a statement of fact - as was his remark about support drifting away from minor parties.

The subliminal message, though, was that minor parties are only trouble and most voters do not back them so they aren't really needed.

The trouble is any new electoral system will not be operative until the 2017 election.

There will be two MMP elections before then. National might not need Act in the longer term.

But it sure needs a revived Act or some equivalent in the short term.