It's been a year, but I finally wrote up my critique of "longtermism" (of the Bostrom / Toby Ord variety) in some detail. I explain why this ideology could be extremely dangerous -- a claim that, it seems, some others in the community have picked up on recently (which is very encouraging). The book is on Medium here and PDF/EPUB versions can be downloaded here.
I don’t have time to write a detailed and well-argued response, sorry. Here are some very rough quick thoughts on why I downvoted. Happy to expand on any points and have a discussion.
In general, I think criticisms of longtermism from people who 'get' longtermism are incredibly valuable to longtermists.
One reason if that if the criticisms carry entirely, you'll save them from basically wasting their careers. Another reason is that you can point out weaknesses in longtermism or in their application of longtermism that they wouldn't have spotted themselves. And a third reason is that in the worlds where longtermism is true, this helps longtermists work out better ways to frame the ideas to not put off potential sympathisers.
Clarity
In general, I found it hard to work out the actual arguments of the book and how they interfaced with the case for longtermism.
Sometimes I found that there were some claims being implied but they were not explicit. So please point out any incorrect inferences I’ve made below!
I was unsure what was being critiqued: longtermism, Bostrom’s views, utilitarianism, consequentialism, or something else.
The thesis of the book (for people reading this comment, and to check my understanding)
“Longtermism is a radical ideology that could have disastrous consequences if the wrong people—powerful politicians or even lone actors—were to take its central claims seriously.”
“As outlined in the scholarly literature, it has all the ideological ingredients needed to justify a genocidal catastrophe.”
Utilitarianism (Edit: I think Tyle has added a better reading of this section below)
Millennialism
Mere Ripples
White Supremacy
The book goes on to say:
Genocide (Edit: I think Tyle and Lowry have added good explanations of this below)