The defection of former South Australian Liberal leader Martin Hamilton-Smith to the state Labor government as an independent Liberal cabinet minister has caused outrage among his former colleagues.

He has broken the golden rule of major party politics in Australia by swapping sides. If the boot was on the other foot Labor’s reaction would have been the same.

Hamilton-Smith has switched shortly after an election, and in a way that not only shores up the Weatherill Labor government in a hung parliament – condemning the Liberals to another four years in opposition – but gives him a cabinet position that all his former party colleagues covet.

Not surprisingly, his action has been condemned as treason. Former Howard government minister, Peter Reith, described it as “a gross act of betrayal”.

Hamilton-Smith is not the first MP to take such a step, though he is one of the more senior.

In recent times Labor in South Australia has strengthened its position by including in its cabinet not only a Nationals MP, Karlene Maywald, but also an independent Liberal (and former Liberal), Bob Such, and another independent. It has almost become the South Australian way.

Other independents, including Michael Moore in the ACT, have also joined cabinets, in his case the Carnell Liberal government.

Most notably, the Gillard minority government at the federal level was supported by independents with party backgrounds as MPs – former National Rob Oakeshott and former Liberal Peter Slipper – as well as independent Tony Windsor, a one-time Nationals pre-selection candidate.

There are other examples but they have involved swapping to or from a minor party.

In South Australia Labor’s Kris Hanna moved to the Greens. Several LNP members have moved to the Palmer United Party in Queensland. Most notably, former Australian Democrats leader Cheryl Kernot switched to Labor.

Such swapping still causes heartache and accusations of betrayal, even though in Kernot’s case she resigned her seat and stood for Labor at the next election.

But nothing quite matches swapping sides from one major party to the other.

And, of course, Australian political history has been dotted with party splits, largely in the Labor Party, which have led to MPs, including premiers and prime ministers, crossing en masse from one side to the other. Billy Hughes and Joe Lyons started their parliamentary lives with Labor.

In the 1950s Labor lost federal and state MPs to the new Democratic Labor Party, though these MPs effectively condemned themselves to exile and ultimate defeat rather than the reward of high office. They, like many before and after, were condemned as Labor ‘'rats'' for deserting their party.

Team loyalty and the alleged crime of defection is not restricted just to party politics. It is society-wide. The awful sectarian tension that blighted Australian society for so long was based on an equally deep divide between varieties of Christianity, Protestantism and Catholicism.

The same is true in sporting competitions, whether the Holden-Ford divide in motor sport or the club loyalties in football codes.

If anything matches the intensity of the party divide between Liberal and Labor in South Australia, for instance, it is the dislike, bordering sometimes on apparent hatred, between supporters of Port Adelaide Power and the Adelaide Crows. Many of these tensions, as in politics, are overlaid by social class, geography and educational difference, but some have no basis at all.

Alleged deserters in politics, sport and religion are often vilified because they are a threat to a system that is based on exaggerating the differences between the two sides.

In politics it is even argued that the policy differences between the major parties have declined in recent years. These claims of policy convergence are exaggerated, but it is true that social background differences have narrowed and market economics has captured both sides.

Extreme party discipline reinforces the differences in parliament. Labor MPs take a pledge of solidarity and Liberals behave as though they had.

They vilify each other and punish any MP who has the temerity to cross the floor on legislation. The punishment may be subtle. Even when these MPs are not threatened with dis-endorsement they are regarded as not being team players and often passed over for promotion to ministerial ranks.

Hamilton-Smith’s defection after 17 years should be seen in this light.

Rather than recognising what parties and individuals have in common, party politics is based on competition rather than consensus. It has its origins in human psychology rather than philosophy. Adversarial politics, which sees no good in the other side, is encouraged by a news media that invariably emphasises disagreement over co-operation.

Reith went on to allege that the Hamilton-Smith case “revealed that some politicians barely know the difference between Liberal and Labor”.

He is blind to the fact that some of these differences are exaggerated, even manufactured. There is overlap between the major political parties and some individuals would feel comfortable enough on the other side, though they dare not even whisper it. All parties are a mixture of moderate pragmatists and hard-line ideologues who police the boundaries.

In any individual case of defection, motivation will vary. Personal advancement will mix with principle. Careerism will jostle with the common good. Opposition is the worst place to be in politics so the promise of a cabinet position will be as attractive as the promise of a premiership to a football player who has spent their career in a bottom team.

But the wider picture is more important. The South Australian cabinet will probably be stronger with Hamilton-Smith’s inclusion if he can assimilate to a new culture. Furthermore, the weaknesses of adversarial politics and the often manufactured gulf between parties need continued questioning.

John Warhurst is an emeritus professor of political science at the Australian National University. An earlier version of this article appeared in The Conversation.

John.Warhurst@anu.edu.au