I get the constructive criticism and explaining why you don't like something but just plain complaining…
True. There's a vast difference between making a valid complaint and just plain whining.
Valid complaint: TOEI flubbing a scene by adding filler that deviates from the manga and someone pointing it out that changes the meaning of the scene completely.
Whining: Someone just dropping in and posting something like "Argh horrible episode again. TOEI ruined everything, the anime sucks!" etc.