Instead of talking about the dangers of anonymity, I think we need to reframe the argument in terms of the dangers of social credit score. I don't mean dangers from authoritarians, of course. Everyone understands how the Chinese system is terrible, for instance. I mean the dangers of a "natural", "emergent" social credit score. The kind that you get for free when you attach a way to establish who is who to otherwise anonymous messaging.
It is a problem of trust.
Humans are very trusting. I don't mean this in the sense that we are naive, but rather that we perform an enormous amount of our decision making on beliefs whose veracity we have not established with experiment or argument or proof, but on the basis that someone who you trust believes it too.
This is a very convenient heuristic, as otherwise you probably wouldn't be willing to get on an airplane, but it has very serious implications when a wrong idea gets too much traction, and now suddenly everyone believes it only because everyone else believes it. What does this have to do with identity, you say? Well, if you don't know who said something, you don't know whether or not to trust it. No one (well, almost no one) trusts something just because it is written down somewhere. The aggregate amount of identity floating around is an upper bound on how much belief that can be created exclusively by the trust mechanism.
Moreover, trust is increasing. This is a little abstract, but if there is a belief that tends to only be expressed by the people I trust, and someone expresses that belief, I gain a little more trust in that person. I have added trust to the system. Note again that this would be impossible in a completely anonymous system.
One would hope that the breaking of trust was transitive in the same way that the gaining of trust is transitive. If I discover that you actually believe something wrong, or you want to hurt me, or any of the dozens of things that mean that I shouldn't trust you, then all of the things that I believe because you believed them get put back in the queue. These beliefs should have to be rejustified.
Unlike in the trust creation process though, this is essentially impossible. Not only do I have to go back and find out all the things that I believe because you believed them, but also find the things that I believe because someone else trusted you and I trusted them, and so forth. If the community is small enough, it is possible to regroup and redo the corrupted calculations, but the upper bound on that is obviously very low. Really the reason that trust can still survive is that the social penalties for lying from a highly trusted position are that you do not get to participate in the gains from trade that being so trusted provide. Again, if you are a doctor, you lose your entire livelihood if people do not trust you.
So there are two factors that influence whether an epistemological system of trust can survive the interference of trusted liars. The first is how rare trusted liars are, and the second is how much total trust there is in the system. A system which is trusting enough can be completely obliterated by even very rare trusted liars. If your community is the size of the internet, and as fundamentally predicated on trust as non-anonymous social media has become, then your entire system of belief (based on trust) functionally does not have a chain of custody. This is a crisis of epistemology. Any adversary capable of creating trusted liars is not going to find that they have much trouble doing so.
This brings me to my final point, which is that trust is valuable. It is the very basis of advertising, and they have even gotten bold enough to throw the curtain aside and brand themselves as "influencers". Trust can, and is, bought and sold on the open market. The more trusted you are, the more valuable your betrayal is. A doctor can make more than enough money appearing on talk shows for it to be worth trading their good will.
The devastation that the corruption of the trust mechanism has had on the aggregate belief system has been profound. I think you will struggle to find a belief that is held by less than 20% of people.
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Ultimately, two things are required. One is to pull an immediate 180 on internet "trustworthiness". Increasing aggregate trust is a catastrophe greater than global warming. Move to anonymous or pseudonymous boards immediately and never look back except in grave, well explained warnings of what lies that way. The second is that we must work towards reducing our reliance on trust as a mechanism entirely. This is exactly the opposite of what is taught in school, so I suppose it too relies on our capacity to perform a complete 180.
Even mathematics, THE constructive epistemology, is taught as a bunch of algorithms that you are expected to trust. For most people, even including those who take math in college, this is the only exposure to mathematics that they will ever have.
Science, likewise, is taught as a collection of facts, rather than the process by which those facts were obtained. Perhaps the only non-trust based epistemology that I encountered in my (pre-collegiate) education was in computer science. The-computer-does-what-you-tell-it-to is a pretty profound starting point. It certainly changed my life. I can't imagine that K-12 CS programs haven't been utterly neutered by the education system at this point, but hopefully, you can't bureaucracy away their main feature. It's a chink in the armor at least.