A hierarchy can not exist when people do not accept it

The first hierarchies were not accepted by the people at large. They were enforced by narcissistic individuals taking over the food supply and coercing all of the people in the area who depend upon that food supply to serve them. Only the narcissists at the top accepted the hierarchy, and they accepted it because they were the beneficiaries.

And no, the vast majority of narcissists are luckily quite powerless

Only because the positions of power are already full of other narcissists. These "powerless" ones are the ones sitting in reserve, waiting for their opportunity to be on top - and doing enormous psychological damage to everyone around them while they wait for that chance.

Citation needed

"Goliath's Curse" by Luke Kemp is most of it, but "Hierarchy in the Forest" by Chrostopher Boehm adds some nice details about how egalitarian we were when we still had the ability to effective police these individuals. I would also recommend that you have a look at the works of Dr. Ramani to see just how much damage these people do just with interpersonal relationships: "Don't you Know Who I Am?, "Should I Stay or Should I Go?", and "It's Not You".

The idea is that you absolutely should not have hierarchies and other systems that put individuals into power, as those will inevitably be usurped by bad faith actors, or even more likely, corrupt those granted the power.

And how is this state of being enforced? Narcissists will not just obey the rules because people said so. They will create hierarchies without anyone's consent, and they have a wide variety of methods available to them for doing so when presented with a naive population (which I still maintain that leftists largely are, at this point).

Even if you somehow maintain a non-hierarchical state, but do not remove the narcissists, you will still end up having to deal with the social and psychological damage that narcissists do to everyone around them regardless of whether or not they have any kind of special power over others. Why would you want to tolerate this?

What you propose will just result in a witch-hunt with a lot of collateral damage

Only if you mis-identify the bad actors. Part of educating people about how to reliably identify these people is also teaching them how to not mis-identify someone who is not one of these people.

power corrupts even those that are not narcissists to begin with

This premise is actually just false. The psychology and anthropology makes it plainly clear that power does not corrupt - it merely reveals who a person really was all along. If you actually understood narcissism, you'd understand how they mask their personality so that people don't realize just how self-centered and abusive they are. When you give narcissists the ability to avoid accountability (something that typically comes with power), they loosen or even take off the mask because they no longer need it to protect their status, and it is a lot of effort for them to maintain.

So is basically every platform. I do not have the capacity to host something on my own right now, and most people are on Discord already. Besides that, I've found a way to set things up so that we shouldn't have to worry about tripping over Discord's TOS.

I do eventually want to move the community to another (preferably self-hosted) platform once it becomes a practical option.

A number of ways, but here are the biggest ones:

1. We're narcissist-aware. It's like being tankie-aware, but much broader and more encompassing. Narcissism is unfortunately very common, and unless you have studied narcissism and narcissistic abuse tactics, it is extremely likely that you will be unable to identify them reliably. The lack of empathy that characterizes narcissism is fundamentally incompatible with leftism - they will always sabotage leftist organizations if they are present, even when they do not specifically intend to do so.
2. If you look at the formal study of fault-tolerance in distributed systems, you see that it isn't enough to simply have the right governance structure in order to avoid a state where the system (or community, in our case) is no longer able to function. The ability to reliably identify and correct (or remove) faulty actors is actually more important than the choice of governance structure for a community. A lot of anarchists believe axiomatically that power should always be decentralized, but fault-tolerance as we understand it would actually force us to avoid distributing certain powers to members who are not yet able to reliably identify faulty (and, in particular, bad-faith) actors. Of course, we still want to decentralize power as much as is practical, so we do our best to educate our members so that we can safely distribute power to them.
3. Looking at anthropology, we see that civilization has been a narcissistic endeavor from the start, and they are still in control of essentially all of it. This immediately implies that reform-based strategies can't actually work in the long run. It also implies that a simple regime change will not be sufficient to achieve lasting change. We've got to build a new kind of society which is able to fill the niche currently occupied by civilization as we know it - one which is actually designed to be robust to infiltration and subversion by bad actors from the start.

Hierarchy in the Forest by Cristopher Boehm is literally about this. In short, we've always had some kind of "hierarchy", but starting at about 3 million years ago, and becoming ubiquitous at around 300,000 years ago, we "inverted" the hierarchy so that domineering individuals were ostracized, and everybody else was more or less equal. In other words, we found a way to be egalitarian, despite our despotic roots as a species - and we did it for long enough to significantly impact the human genome.

Then the domineering individuals started to figure out how to undo this and form dominance hierarchies again, starting about 40,000 years ago.

Only 4000 years ago? That is much more recent than I would have expected (I am familiar with humanity's egalitarian roots prior to agriculture, but most everything I know about after the adoption of agriculture are societies that were either always hierarchical, or became hierarchical over time). How did they manage to escape notice from the more aggressively imperialist societies long enough to build such a city? How did they manage to police themselves in such a way as to avoid forming a dominance hierarchy themselves? They would have to have had some way of reliably identifying domineering individuals and acting against them in order to actually reverse the inequality trend like that. How did they ultimately fall?

Also, do you happen to have a link/citation for the academic paper that this article is referencing? I don't even see the name mentioned in the article text - only the author and university.

While people living in past civilizations at their lowest points might be willing to trade places with us, the vast majority of humans for the vast majority of human history would not be. When offered to join the ranks of the civilized world, "uncivilized" indigenous people consistently turn down the offer. They think that we're all insane.

The past 20,000 years are not all of human history. Prior to the development of civilization, life was actually pretty good for most people. They also didn't have to worry about most of the things in that article. The only significant material differences were higher infant mortality, and lower overall material wealth (but this lower material wealth did not mean a lower quality of life, in general, as people's lifestyles and culture were adapted to that level of wealth). The lack of medical care was largely a non-issue, because those people did not suffer from the diseases of civilization, were typically naturally resistant to bacterial infections due to diet, and what infectious diseases did plague them were generally unable to spread very far or very fast because the different groups were not constantly forced to intermingle in tight indoor spaces at large scales.

This whole article reinforces a false narrative known as the "Myth of Progress". This is a very dangerous and toxic myth that undermines a lot of people's reasoning about what the future should look like. This is intentional - the myth of progress is propaganda pushed by the state via school curriculum and academic publication bias (though this latter mechanism is starting to fail - most academics now reject the myth of progress) to warp people's sense of what life could be like.

I would recommend that people read books like "Nutrition and Physical Degeneration" by Weston A. Price, "Civilized to Death" by Christopher Ryan, or "Goliath's Curse" by Luke Kemp to get an overall better picture of the relationship between living conditions in the past versus the modern day.

To clarify, I am not suggesting that life in the stone age (or prior) is the human ideal and that we should go back to that. I am not a primtivist (though I am aware that the collapse of global civilization may limit our options, realistically). I am merely suggesting that we can't assume that life in modern civilization is as much better than life in the past as so many people claim. We should be looking at all of human history and taking the best ideas from all parts of it to inform a model of how we should be doing things going forward. In order to do that, we can't let myths cloud our perception of what the past was actually like.

I think that others have done a sufficient job of answering the main question. I have things to say about the secondary questions:

how badly damaged is it?

I am wondering how it would be possible to reverse or remove that opinion of so many.

I've actually put quite a bit of thought into this problem. Countering the intentional destruction of language in general seems to be basically impossible to do directly because of how many people there are who have no particular interest in figuring out what the word really means, and who just perpetuate the current zeitgeist via sheer inertia. It also doesn't help that there are a great many who claim to be anarchists who actually want the term to be misunderstood. The nihilistic version of anarchism that you're calling out is perfect for sociopathic individuals who want a world without accountability.

My conclusion is that the word itself has become effectively destroyed and unusable (except in contexts where you know that your audience is made of the small subset of people who actually understand what it is supposed to mean) and needs to be replaced. However, attempting to just invent a new term for the same ideas won't quite work either, because it will just be equated to the old one, and destroyed by the very same actors as before. We may be able to buy some time, but we need to do something about the forces that work to destroy the language itself if we want a lasting solution.

We need to learn how to protect ourselves from the actors that consistently sabotage our efforts to communicate, form communities and institutions, and actually accomplish objectives. We need to learn how to recognize those actors reliably, and keep them out of our spaces. Feds and such aren't really the main issue here - it's the people that claim to be our allies but instead subvert our rhetoric and activity to their own selfish ends that we need to be most wary of.

Once we can keep our spaces clean, we'll have control over our language again, and we can use a new term or the old one. Those who are actually interested in doing good can be kept safe from the interference of bad-faith actors as long as they are able to find their way into these spaces.

You want to learn about narcissism, narcissistic abuse, and, in particular, what happens to the victims of sustained narcissistic abuse. The victims end up suffering from 'codependency' or 'self-love deficit disorder' depending on who you talk to. Your mention of 'pathologically stable attachment' is pretty close to talking about one real aspect of codependency. There are attachment disorders (like anxious attachment disorder) that will cause people to hyper-attach to others (especially abusers).

I do not say this to name-call, per se - but rather to give you some keywords that you can use to learn more about what's going on. I will also recommend this youtuber, and in particular her Glossary of Narcissistic Relationships playlist. She's also written books if you would prefer that format instead. Most information on this topic focuses on interpersonal relationships (intimate ones, especially), but it is trivially applicable to other (larger) contexts.

One of the best things you can do for someone who is suffering from codependency is to help them learn about narcissistic abuse, so that they are even able to recognize what is being done to them. A big part of the apathy that you are observing in people is just plain normalization. They literally don't even recognize that they are being abused. Once you get past this barrier, helping them heal from the trauma and develop far healthier responses to abusive situations becomes a whole lot easier.

It's not like it was never alluded to:

"Then as elites extract more wealth from the people and the land, they make societies more fragile, leading to infighting, corruption, immiseration of the masses, less healthy people, overexpansion, environmental degradation and poor decision making by a small oligarchy. The hollowed-out shell of a society is eventually cracked asunder by shocks such as disease, war or climate change."

(bold added to highlight indirect mention of overshoot by other names)

The reason that overshoot isn't really a focus in this article is because the author has recognized (correctly, IMO) that overshoot is just a symptom of a much deeper problem - large-scale domination by narcissistic/psychopathic individuals.