He isn't complaining. It's not the be-all and end-all for some people. I'd much rather be misunderstood than go 'loooooool JK don't downvote guyz!!!' after a joke, which is exactly what '/s' reads like.
Body language and inflections are nuances that are lost in text but contribute heavily to sarcasm.
Also, it's been really difficult these last few years to determine the difference between a blatant joke and someone's perceived reality, which is downright terrifying if you think about it too long.
It's not psuedoscience, it's simply the observation that, as this thread shows, it can often be difficult to tell the difference between satire and honestly held opinions. I question your understanding of the word "psuedoscience," if you think it applies to Poe's Law.
That's not what it means firstly, and secondly sociology is science, semiotics is science, and this waffle is masquerading as similar. Calling it a 'law' and wheeling it out as evidence contributes to that, convincing impressionable nerds that they need to backhand their jokes to avoid the dreaded downvote