But what is the basis for thinking these two concepts are mutually exclusive? Isn't it possible for pluralist formations to have the same problems of sectarianism which Derek and other critics claim afflict 'vanguard organisations'?
Sectarianism isn't the preserve of a particular type of organisation. It isn't even the preserve of people in organisations. A lot of the worst sectarian nonsense I've encountered has been from the proudly non-aligned 'independents' who think that remaining aloof from any kind of organisation inoculates them against sectarianism.
It certainly isn't the preserve of the radical left either. Much of the really pernicious and damaging sectarianism in the labour movement is directed from right to left. Consider recent sectarian attacks by some Labour loyalists on Respect.
When union officials victimise left-wing activists, is that not divisive sectarianism? It is especially bad because the imbalance in power relations means it can have real consequences: this imbalance is nearly always in favour of the right over the left. But it's not just victimisations. You will struggle to find anything on the radical left more unpleasantly sectarian than Unison right-wingers' attacks on 'ultra lefts', while they were selling their own members down the river over pensions.
As for the radical left, the existence of numerous different groups is presented as evidence of a supposedly terrible culture of faction-fighting and pointless splits. But such diversity is more or less the same everywhere, and in all periods in the working class movement's history.
When I went to the occupied West Bank last year I paid an unforgettable and eye-opening visit to the Palestinian prisoners' museum. Above all it was memorable because of the disturbing insights into Israeli abuses of prisoners. But something else stuck with me: my guide, imprisoned during the First Intifada, said that there were 30-40 different radical political groups represented in his prison. Not quite 57 varieties, but getting close.
We can also take at least a little consolation from the knowledge that the far right is even more factionalised than the far left. Reports of a proliferation of new groups on the European far right are widely interpreted as indicating a threat. True, but also ask yourself: why are there so many different groups? This is as much a sign of weakness as strength. They are nowhere near forming a cohesive movement.
The focus on the existence of different groups misses the point about sectarianism. It is possible for several different groups to each operate independently but still work together on specific issues and campaigns (often they don't co-operate - and that DOES reflect sectarianism - but I'll come on to that).
Repeated splits are framed as examples of sectarianism. Yet if there is a split in an organisation then clearly people have previously made great efforts to work together, despite differences, but have now reached a point where it makes more sense to part ways. Anyone who has ever been through a split on the left knows how difficult an experience it is - and that it's very much a last resort.
It should also be obvious that pluralist political formations - from the Labour Party to the Green Party - don't preclude the kind of divisive behaviour we associate with sectarianism. There are factional attacks within such parties and what might loosely be described as 'tribal' attacks on those from other parties (despite common ground politically).
My definition of sectarianism on the Left has three elements.
Firstly, there is a focus on difference at the expense of common ground, leading to an unwillingness to join forces and work together. Secondly, disputes in the past determine who works with whom (or, more accurately, who doesn't work with whom). Thirdly, a focus on the internal dynamics of the left is divorced from external political reality.
The first of these is, I suppose, the classic defining feature: this refusal to co-operate even when we have the same objectives (note: this is not the same as arguing and disagreeing, which are entirely healthy). A sub-element of this is the habit of elevating secondary issues to a status they don't deserve, clouding what really matters. Relatively trivial disagrements become a barrier to unity.
The second feature refers to how socialists often allow past disagreements to determine who they will and won't align with. A great example of overcoming such past divisions, in a commitment to non-sectarian unity, is the williimgness of Trotskyists and Communists to co-operate in founding and developing the Stop the War Coalition from 2001 onwards, alongside many activists from neither tradition.
The third element is less obvious, but almost always appears as part of sectarianism. It is an excessive focus on internal structures and the doings of the organised left, rather than considering how activists can relate to the outside world. Sectarian attacks on the revolutionary left almost always involve denunciations of 'Leninism' for alleged undemocratic practices, which are supposed to justify not working with such groups. Sectarian disputes always seem to have a trivial focus on organisational matters (rather than real political substance).
All the other familiar elements of sectarianism - bitterness, personal attacks, irrelevant sniping etc - are secondary elements, which follow on from those main features. Furthermore, sectarianism is itself more symptom than cause. It is rarely the root of the difficulties we encounter (though of course it can develop a self-sustaining momentum).
There is no doubt, I should stress, that sectarianism is a genuinely damaging poison. In Newcastle, where I am politically active, it is the greatest obstacle we face in building a bigger, stronger Left. The abandonment of sectarianism would lay the ground for nothing less than a transformation of the left's fortunes.
The point is that sectarianism is political and context-dependent. It isn't simply some strange disease that mysteriously afflicts socialists. Sectarian behaviour emerges as part of a wider political problem.
Take, as a current example, the Socialist Party's refusal to support voting for Ken Livingstone for mayor of London, despite the fact that Londoners face (in reality) a two-horse race between Livingstone and Tory Boris Johnson, with no candidate of the radical left. (This is a trival example because the Socialist Party will hardly have much influence over the outcome, but it is good for illustrative purposes).
It is sectarian silliness, a failure to identify the principal enemy. But it is politically conditioned sectarianism.
The Socialist Party overstates the decline of Labourism. It also wrongly sees Labour as substantially no different from the Tories, overlooking the huge differences in the social base and political views of their respective members and supporters. And it over-estimates the prospects for building independent electoral formations in the current period. All of this leads it to a misguided position.
The alternative to sectarianism is not 'pluralism'. It is a commitment to building unity in action around common objectives, while respectfully arguing about issues where we differ and sustaining
whatever independent political groups best reflect our views. That seems a healthy non-sectarian approach to me.
In practice, the best way of combating sectarianism is almost always the same: get beyond the snipers and organise with wider layers of people, many of whom aren't part of the traditional 'left'. The narrow project of uniting existing left-wing fragments is ultimately less important than renewing the left by building outwards and involving new generations of activists.