The author of that blog is definitely reaching . . . he complains about how Barker is being treated currently, and then spins a yarn to try and find a narrative that fits into the "Barker is OK" position.
But he does bring up good points. One of the reasons why the news of "Serpent's Walk" is so troubling and surprising to many Barker fans is it seems incongruous with other aspects of Barker's life. There is more unknown about Barker's engagement with Nazism than there is known.
Barker is gone, we can't ask him WHY he wrote "Serpent's Walk". Was it to explore his own Nazi sympathies? Or just a story that sprung from the recesses of his mind? A literary hoax? A sci-fi novel that explores Nazi characters and themes without the author endorsing those ideas?
But still . . . the disappointment, anger, and sadness aimed at Barker is legitimate and fair. As
@darjr said, Barker was well aware of the problematic nature of his novel, and decided to not only publish it anyway, but to go through the whole "literary hoax" idea of creating an alternate persona, engaging with an anti-Semitic journal . . . ugh. Barker went through a lot of work to publish a very problematic novel, all fully aware of what he was doing. And yet, to choose a pseudonym so close to his own name . . . I don't think Barker would be surprised at the reactions he's getting today.
Barker was either a Nazi sympathizer, or as put forth way earlier in this thread, Barker was "that guy". An intellectual so detached from society that he thought writing and publishing this novel was a fine idea for a "literary hoax". I have little sympathy for the man or his legacy.