I accept that neither of the things I listed logically lead to accepting the value claim made in the argument (other than that the effective altruism movement generally assumes one's circle is at least as wide as "all humans", considering the emphasis on charities working a continent away), but I still feel quite confident that LessWrongers are likely, and more likely than the general population, to accept said value claim - unless you want to argue about expected values, the assumption made seems to be "the width of the reader's circle extends to all (meaningfully) sentient beings", which is probably a lot more likely in a community like ours that reads a lot of sci-fi.