How opposed are we as anarchists to vanguard organizations? And how ought libertarian vanguards be organized?

A Vanguard as I understand is only applicable in a Revolutionary situation where the State forces have been subdued and the Libertarian forces use a Vanguard to finally destroy it.How long it remains depends on how advanced the Working Class is politically,militarily,theoretically etc.

I mean, I suppose one point to note is that, while the FAI did its job well for a time, it did also kind of fail - on another thread you mention the formation of the Friends of Durruti as a militant anti-collaboration tendency, but they wouldn't have needed to exist as something separate if the FAI had been doing its job properly. So even groups that are set up specifically to play this role can end up with their members joining the government.
Beyond that, I'd tend to lean towards a kind of "organisational pluralism", by which I sort of mean that there's a whole number of tasks that need doing for a successful revolutionary movement to be possible: discussing and developing theory, fighting the police and other opponents in the streets, organising mutual aid/social reproduction work to meet people's day-to-day needs, co-ordinating the class struggle in the workplaces, and so on. Some form of organisation, whether formal or informal, will be needed for all of these tasks. I suppose the "vanguard" position would be that each of these tasks should be formally united under the banner of a single organisation, but I'd ask what the actual benefits are of having them officially centralised in such a fashion. Gping back to Spain, I think you can see examples of this approach as well: the Nosotros group, the Mujeres Libres and others certainly played positive roles, but I don't think it would make sense to describe them as a "vanguard", more one group among others.

From what I have read it was a certain section of the FAI - the barcelona based - which was drawn into aping the Leninist ways in adopting vanguardist ways - seizing control of various CNT important committees and most importantly mass circulation CNT newspapers via wild slandering of other factions in the CNT such as the Trientistas and the BOC later merged into POUM - as a result of these key positions they encouraged the insurrectionary gymnastics of the early 30's which led to waves of massive state repression and precluded the CNT developing a more realistic revolutionary strategy which would have avoided the collaboration in the Republican State/Govt. and role in the counter revolution in the Republican/liberated sector during the Civil War. (See Benjamin Martin's "Agony of Modernisation')
In the book 'Living Anarchism' the Life of Jose Periats. It refers to most in FAI being opposed to the above vanguardist stuff and holding some big conference try to stop it. Those most involved in the vanguardism didn't turn up. So definitely vanguardism is completely inappropriate. In the Anglo world today - most important is to become a 'catalyst' in the workers movement to facilitate workers self organisation and direct action and facilitating strike waves leading to the emergence via a complex process to mass syndicalist unionism. So as to prepare workers for the overthrow of capitalism and avoiding a new ruling class emerging. As occurred in the Bolshevik vanguard takeover in Russia in 1917. Such a catalyst would be the interweaving of networks on the job and outside the job focusing on long range strategic organising. Self eduction is very important for those in these networks - making a serious study of the workers movement and its currents, etc.
However, today in the Anglo World - many so called anarchist groups and federations often ape the Trot groups in many respects - due to the social base eg students, middle class elements and the sprinkling of demoralised workers - most heavily influenced by identity politics via the universities and middle class 'oppression mongering' and the low morale of workers in many sectors due to the progress of the employer offensive. When these people see 'Anarchist Group' they see stuff that is not supposed to be there - excuse for social occasions/opportunity for dope smoking/sex orgies/pseudo church, etc. They read little or nothing re anarchism or any much else. They have little grasp of serious workers control directed activity. Also you must take account the extreme marginality of anarchism as a current in the revolutionary workers movement for 4-5 decades in the 20th century and the predominance of mass stalinism with the communist parties and then the trot/Maoist groups to the left of the social democratic set up in this period. The whole left political culture oozes with this poison. See Review of A Beautiful Idea. History of Freedom Press in RW Vol.37No.2 (225) Aug-Sept 2019 on www.rebelworker.org which looks at some of these issues.

Well I think organising a militant minority is fairly uncontroversial, and pretty much universally accepted among all anarchist tendencies, except perhaps individualists and some insurrectionists. Generally when looking at stuff about vanguards its best to judge by context what they're talking about and look at the details, not just the label -- I mean there used to be anarchist organisations who'd emphatically state they saw themselves as a vanguard, but not in the sense that Marxists use the term, to mean a small group that will take the reins so to speak.

Anarchists oppose the monopolisation of a revolution by a small group, that seeks to take control of it and use it for their own ends. The most typical example cited is that of the Bolsheviks during the Russian Revolution. But leadership doesn't have to mean taking control, or constituting ourselves as an authority; we can lead by example, pushing people to organise and ensuring that libertarian structures predominate.

In terms of organisation here and now, conditions vary so widely that it's impossible to suggest one uniform approach that all should follow. In one place, it may make more sense to encourage a broad anarchist federation, in others it may make more sense to focus on small, more specific groups, or a network of militants like ASN describes, and so on. I'm a syndicalist so naturally lean more towards ASN's idea but I recognise there's no one answer here.

On the FAI -- in my opinion it's oversimplified to say they led the anarchisation of the CNT. They had a different role. As ASN points out they weren't a uniform organisation, for the most part they were a federation of different affinity groups, that would naturally have differences of opinion amongst each other. Their role within the CNT is usually framed as leading a battle between anarchists and reformists, but I think all of the "reformists" they were up against ("old guard", Trientistas) explicitly and emphatically identified themselves as anarchists and organised as such; except maybe Pestaña who by the end of the dispute had created his own party organisation. And several of the key FAI militants ended up leading the charge for governmental collaboration when the war kicked off.

So, it's not always that simple. The FAI played a very positive role at times and that shouldn't be denied, but their case also demonstrates the problem of seeing organisation like a panacea; even once you organise a group, you still need to act within it (and sometimes against it) to ensure libertarian principles are being upheld.

Quite old, but the one and only time (that I can recall) an American anarchist group using the term "vanguard". Both as a name of their group and their publication.

In issue one of their publication, they explain the role of "the vanguard" from a libertarian perspective.

https://libcom.org/library/vanguard-vol-1-no1-april-1932

The term vanguard has connotations - less so is the word avantgarde

It's the same word

That is my exact point, fluffy.

Same word but one has a negative connotation but the other not so much.

Political vanguard
Political avantgarde

Isn't there a slight difference in the tone?