Neo-reactionary ideology seems like a close match for fascism. The Wikipedia article on it discusses whether it is or isn’t fascism: https://en.wikipedia.org/wiki/Dark_Enlightenment

Two major themes of neo-reactionary ideology seem to be authoritarianism and white supremacy.

There is definitely some overlap between people who identify with neo-reactionary ideas and people who identify with explicitly neo-Nazi/neo-fascist ideas.

I should probably stop posting on this or reading the comments, for the sake of my mental health (I mean that literally, this is a major anxiety disorder trigger for me.)

I am with you on this. I have had to disengage for mental health reasons. This stuff affects me quite seriously. I may or may not check back in on this post again. I may have to go as far as completely disengaging from the EA Forum on both this alt and my main account for an indefinite period, maybe forever. 

i don’t know your specific situation, but I will speak on a general dynamic. 

The psychologist Elaine Aron has a hypothesis that there is a neurological subtype called the Highly Sensitive Person that is unusually sensitive to sensory and emotional stimuli. This can include being unusually unsettled if other people appear to be in pain or discomfort or unusually disturbed by depictions of violence or suffering in TV or movies. 

Some have suggested that Aron is describing autism or a form of autism. I’m not sure what’s true. Some people and some psychometric tests have told me that I’m a Highly Sensitive Person and that I’m autistic. 

Aggressive environments or aggressive subcultures can shake out people who are particularly sensitive in this way. When that happens, I believe a certain kind of wisdom and temperance is lost. The soft, gentle side of people must be preserved and a community should be such that particularly soft, gentle people can be included and welcomed without losing their softness and gentleness.

Aristotle talked about practical wisdom (phronêsis). "Practical wisdom" makes me think about the contrast between my analytic philosophy courses in ethics and the social work elective I took in undergrad. First, the atmosphere of the courses was just so different. The philosophy classes usually felt kind of cold, sometimes kind of mean. Social work was a culture shock for me because the people were so palpably kind and warm. Second, my social work professor had been involved in real moral issues deeply and directly. Those included HIV/AIDS activism, dealing with violence in schools, and counselling couples navigating infidelity. I was so impressed with his practical wisdom. How do I assess that he had practical wisdom? I don’t really know. How do I decide when an ethical argument seems rational? I don’t really know, either. 

The contrast between my ethics courses and that social work course is a microcosm of so much for me. It’s that same contrast you see in the EA movement where, for example, you have the absurd situation where people take the principle of impartiality or equal consideration of interests so seriously that they concern themselves with shrimp welfare but, in practical terms, their moral circle doesn’t fully include women. 

Tying it all back together, a movement that can’t align itself:

• with democracy, against fascism 
• with women, against sexism 
• with people of colour, against white supremacy
• with core moral decency, against Nazis 

is morally bankrupt, has lost the plot, jumped the shark, utterly, disastrously failed. 

One part of the causal story of how that could happen is if you have an influential element of the subculture that disdains softness and gentleness and disdains soft, gentle people. I don’t think you can have future-proof ethics if you don’t, like, care about people’s feelings. 

Going a step deeper, I think people’s disdain for empathy and sensitivity often involves a wounded, tragic history of other people not treating their feelings and experiences with empathy and sensitivity and an ongoing sense of grievance about that continuing to be the case. A lot more could be written on this topic, but I don’t have the time right now and this comment has already gotten quite long.

The macro question is what to do about white supremacists in general in society. I will leave that topic to another place and time. 

The micro question is what to do about white supremacists on the EA Forum. I think we should ban them.

I think @titotal very eloquently described the Nazi death spiral problem. If you don’t take a hard stance against white supremacists, you signal your welcomingness to white supremacists and you signal your unwelcomingness to people who don’t like sharing a community with white supremacists. This runs the risk of a range of bad outcomes from severe reputational damage to destroying the effective altruist community as we know it. 

Something else I haven’t mentioned about preventing the Nazi death spiral and why "just debate the Nazis" is not an adequate way to prevent the Nazi death spiral:

If they don’t get banned for posting Nazi stuff, the Nazis can become part of the community  by posting other, more normal EA-type stuff. People can read and upvote and comment on the normal stuff without knowing about the posters’ Nazi affiliations or beliefs. Then, you have users with a lot of karma who are Nazis, and people will look around at the EA community and say, "Hmm, there sure are a lot of Nazis here!" and then leave.

I don’t think effective altruism is a covert racist eugenics cult like some critics seem to claim, but there are people out there who would love to turn effective altruism into a racist eugenics cult and I don’t think we should hand them our movement on a silver platter. 

Ban the Nazis. 

A short summary of my above comment: 

1. White supremacists and Nazis disguise their views to make them seem more benign and acceptable, but you can often find connections to overt Nazism and/or white supremacy without looking super hard. Ives Parr disguised his views and I showed the connections to overt Nazism and white supremacy in the OP.
2. Expecting people to debate white supremacists and Nazis is unfair and harmful, as well as damaging to the community. Just ban them. 
3. The EA community has more racist behaviour than I can feel proud of. This makes me sad. I suspect a survey of people of colour with experience of EA would confirm EA has a racism problem. 

I would have even less energy if I felt the upshot of these discussions was a set of policy proposals that seemed abhorrent to me/ felt like a dicsussion of my value as a person.

I think this is the key thing. 

First, people are highly motivated to disguise ideas that have already been rejected, although they often disguise them very thinly. Here’s an example from when "creationism" got rebranded as "intelligent design" in the United States. The example focuses on the anti-evolution textbook Of Pandas and People:

Working late one night, I discovered a crucial difference between the two 1987 drafts [of the textbook]: one was written before the Supreme Court’s 1987 Edwards v Aguillard decision outlawing creationism in public schools, and the other was obviously written afterwards. The first version contained blatant creationist terminology. In the second, creationist terminology had been deleted and replaced by "intelligent design" and other ID terms. A new footnote in the latter version referenced the Edwards decision, indicating a conscious attempt to circumvent the Edwards ruling in the revised manuscript that would become Pandas. The "search and replace" operation must have been done in a hurry: in the post-Edwards manuscript, "creationists" was not completely deleted by whoever tried to replace it with "design proponents". The hybrid term "cdesign proponentsists" now stands as a "missing link" between the blatantly creationist earlier drafts and the post-Edwards versions of Pandas.

Roger Pearson, who ran Mankind Quarterly from 1978 to 2015, made some rather feeble attempts to disguise his ideas, such as this one: 

Pearson’s own assistant during the conference was Earl Thomas, a former storm trooper in the American Nazi Party, and when forced to expel two men distributing anti-Semitic literature from the National States Rights Party, he was quoted as telling them, “Not that I’m not sympathetic with what you’re doing … but don’t embarrass me and cut my throat.” He then asked them to give his regards to the secretary of the party.

The main point of this post was to remove the thin disguise that Ives Parr put over his ideas. It seems either I did not succeed or the user base of the EA Forum is disturbingly tolerant of white supremacy, or perhaps some combination of both. 

Second, the discussion and debate of, e.g., coded white supremacist ideas exact a cost on some participants that they do not on others. (A hypothetical "Let’s decide whether to kill Concerned EA Forum User" thread would demonstrate this principle in the extreme.) It’s more than exhausting, it’s acutely distressing to defend your rights as a minority when those rights are under attack. It can also be exhausting and distressing for others who feel the injustice strongly to participate in such debates. Avoiding or disengaging becomes simple self-preservation.

People self-select out of these debates. I think the people who are able to coolly and calmly, ad nauseam, debate, e.g., whether Hitler had a point about the Jews are typically the worst positioned to form good opinions on these subjects. They have the least empathy, the least moral concern, the weakest sense of justice, and are most detached from the reality and actual stakes of what they’re talking about. 

Many people enjoy provoking and offending other people. I think this is very common. Some people even enjoy causing other people distress. This seems to be true of a lot of people who oppose minority rights. The cost is not symmetrical. 

Allowing debate of, e.g., white supremacy on the EA Forum, besides being simply off-topic in most cases, creates a no-win situation for the people whose rights and value are being debated and for other people who care a lot about them. If you engage in the debate, it will exhaust you and distress you, which your interlocutors may very well enjoy. If you avoid the debate or debate a bit and then disengage, this can create the impression that your views can’t be reasonably defended. It can also create the impression that your interlocutors’ views are the dominant ones in the community, which can become a self-fulfilling prophecy. (See: "Nazi death spiral".)

Third, I would like to see a survey of various demographics’ impressions of the EA community’s attitudes about people like them, but I don’t know how you would be able to survey the people who joined then left or refrained from joining because of those impressions. The questions I’m imagining would be something like, "How likely do you think EAs are to support abhorrent policies or practices with regard to people of your race/gender/identity?" or "Do you think EAs see people of your race/gender/identity as having equal value as everyone else?". 

I suspect that, if we could know the answers to those kinds of questions, it would confirm the existence of a serious problem. EA was founded as a movement to escape banal evils (e.g. the banal evil of ignoring the drowning child), but with regard to some banal evils it is quite morally unexceptional. I think the moral circles of many EAs do not encompass other human beings as fully as they could. It’s easy to nominally support universal human equality but fail to live up to that in practice. What I see EAs saying and doing with regard to race and racism is just so sad. 

Universal human equality is a point of core moral integrity for me (as it is for many others). I can’t imagine wholeheartedly supporting EA if universal human equality is not a strong part of the movement. 

Imagine someone runs up to your house with a can of gasoline and some matches. They start talking about how there are bad men living in your walls and they need to burn the place down. Now, the fact that this person wants to burn you house down doesn’t allow you to determine whether there are bad men hiding in your walls. But focusing on that epistemological point would be a distraction.

The salient thing to notice is that this person wants to burn your house down. 

you can’t determine the truth about an aspect of reality (in this case, what cause group differences in IQ)… by looking at which political agenda is better.

David definitely wasn’t saying that you can determine the empirical truth that way. If that’s the claim you think you were responding to, then I think you misinterpreted him in a really uncharitable and unfair way.