Spinrad's "Third World Worlds" falters at two points. The first is his introduction: his thesis can be summed up as "American/British writers writing about other countries." What's drawing the ire of most people, however, are his opening lines, everything from his unfamiliarity with science fiction outside of the First World to Octavia Butler not being African American. This fails because most people don't even get to Spinrad's main argument: they're already incensed by his faulty opening. His entire discourse on Third World countries and Mike Resnick is honestly there to prepare the reader for the succeeding paragraphs and not his main points. If we edit the article for example and started with "Paul McAuley is a British writer...", Spinrad's thesis would have remained intact and wouldn't have resulted in this week's conflagration. Nick Mamatas would have still called him on his interpretation of Ian McDonald's Brasyl, and Saladin Ahmed would have still rightly summed it up as "Please, please, please, if you are not Brazilian or Thai or Turkish, don't tell me how convincingly or authentically American (or British) author #3462 depicts Brazil or Thailand or Turkey!" but at least it wouldn't be this big of an issue.
That's not to dismiss Spinrad's opening paragraphs. They are legitimate concerns but when you analyze it, the article could have discarded them. With their inclusion, however, Spinrad is operating from a false supposition. If this were fiction, it's akin to Spinrad writing a murder mystery except his prologue doesn't actually result in the murder of any victim, without which, there can be no investigation that drives the rest of the narrative (and it's not the type of investigation that ends with "he/she was never murdered to begin with!").
The second failure of Spinrad is what he focused on. For example, we have this contentious paragraph:
"So, for now at least, and in the apparent absence of a significant body of science fiction written by born and bred Africans, this Caucasian American is probably the closest thing there is or has been to an African science fiction writer, with the exception of Octavia Butler. Who did write the same sort of thing, and did it well, and was Black to boot, but I use that politically incorrect word rather than “African American” because aside from her genetic heritage she was no more African than Mike Resnick."Spinrad could have elaborated on this further and made it his central thesis, instead of talking about other American and British writers and their Third World fiction. It wouldn't make him any less erroneous, but at least the controversy would have been intentional, instead of a throwaway paragraph.
In fiction, this is the equivalent of creating a very compelling character, and making them an extra. In Star Wars, it's like demoting Han Solo to a random rebel that dies in the initial skirmish.