My first thought is that in the part I know best (the rationalists and economists with blogs), sneering at people who see connections and mutual influence as conspiracy theorists is dead wrong. Its a fact that leading thinkers hung out on the Extropians mailing list in the 1990s and later became publicly enthusiastic for ideas which former buddies had promoted in the 1990s! Its a fact that of the three most prominent rationalist bloggers who are not economists, two have expressed enthusiastic support for scientific racism (and a very young Bostrom did so, and his recantation suggests that he is still interested just not sure about the 'genetic' part). Its elementary that people often adopt ideas from their friends, family, and lovers, one basic form of political lobbying is to organize nice meals or parties, invite fellow travellers and the people you want them to influence, and let nature take its course. No one person in this space has the same terrible ideas or sinister goals, and its not reasonable to ask a member of the public to keep straight the difference between Eliezer Yudkowski and Robin Hanson.
Edit:
A random look at Caroline Ellison's Tumblr showed me a post which begins "btw a link from SSC sent me down a rabbit hole of reading (scientific racist blogger) hbd chick and related links lately and the whole intellectual edifice is pretty fascinating. I don’t have a great summary, and epistemic status tentative so you should just read the blog and follow the rabbit hole yourself. "
I can not speak to longtermism since I have not read key works and do not know the key figures. So I can't say how well the Internet criticisms represent it. There may well be some conspiratorial thinking in Torres and co's belief that small passages show a hidden agenda. But I have seen Caroline Ellison's tumblr blog computing the suffering of fish on a scale with the suffering caused by specific human diseases, and everything I know about singulitarianism screams "run. Do not engage. Its a trap for minds like yours, in the way that a confidence game is a trap."
OTOH, I agree that I have not heard of any major sinister Transhumanist groups and I have never heard of Cosmism or Extropianism. I also agree that some of the critics have a beef against utilitarianism, which can be a useful ethical framework if you don't go too far.
"Perhaps the best example of grounded, careful thinking on these topics is Nick Bostrom’s book 2014
Superintelligence," Ceglowski is not an intellectual but his takeaway from that book was that it was designed to catch people with a weakness for clever ideas.
"An attack on rationalism has to be understood in light of the postmodernist critique of rationality." No, most of us who run screaming from those people (and especially from the LessWrong crowd) are scientists and makers who, as Evans said, deeply distrust their building of castles on the clouds before they set a single stone upon a stone on earth. I agree that its common for people in these spaces or adjacent ones (eg. Michael Shermer or Richard Carrier) to ignore Hume and argue that the one true morality can be deduced from the study of the world by formal logic. But Kant and Hume are not postmodernist thinkers!
"we see its connections to reactionary (as opposed to liberal or centrist) political views as exaggerated" The Rationalism of the Rationally Speaking podcast is full of young sheltered Right Libertarians, polls of the SlateStarCodex readers show that active commentators skew right or right libertarian while readers are more like a sample of the US population. See also Robin Hanson and the Marginal Revolution guy, or Peter Thiel's funding of MetaMed and Yudkowski's foundation (this essay describes Thiel as a Transhumanist but he has funded Yudkowski's flavour or rationalists).
One of the key points of Dan Davies' Lying for Money is that fraudsters want you to be overwhelmed with a million details, while successful prosecutors want you to focus on the broad outlines of the scheme. I think that is what critics like Timnit Gebru or Maciej Ceglowski are doing. Its fair to tell the average person to run screaming whenever a 'rationalist' or longtermist wants them to do something in the real world. Its not reasonable to spend endless time arguing semantics about individual thinkers' politics or exactly which of these terrible ideas they support at a given time. I think they are tarring the innocent and the guilty with the same brush, but I think they would say "yes this is unjust but it will force the decent people to distace themselves from the rationalists and longtermists if they want to get anything done offline."
Edit: Hughes, the author of the Medium piece, co-founded his organization in Boston (yellow flag for this family of ideas, its not so infected as SoCal NYC or Oxford but close) with Nicholas Bostrom (red flag!)
https://en.wikipedia.org/wiki/Institute_for_Ethics_and_Emerging_TechnologiesEdit: so TL;DR I think that
Evans' approach to these spaces as a social space where people adopt each others' unusual ideas and support each others' hilariously doomed projects is the best I have found; maybe supplement it with one of the early criticisms of the singularity or the AI as god by a pop culture figure such as Doctorow. Don't let the drama and the "he said, she said" distract you from the key point that many rationalists and longtermists support some disturbing things and have a history of failure whenever they try to do anything other than post on the Internet and hold geeky social events.