However, I am also getting the impression the real motivation behind these outrageous doom sayers is a few people's malicious propaganda, trying to damage these two's standing vis-a-vis Davis/White on the internet, their real rivals - creating a non-existent impression that these two shouldn't come back. Plus, their real rivals, the Americans, are actually struggling even without injuries - lost count how many times they went flat on ice this season, thus gave judges a hesitation in making them the dominant team. I think these people are really worried and secretly upset that Davis/White just won't be given a carte blanche for the World Championship in Tokyo and of course, these "fans" will deny it and pretend they love and like Virtue/Moir in reality they really wish they would just stop skating, retire or split.
Many of skaters' fans are like that to their rivals: it's nothing new. Although I've seen what you mentioned to be abundant D/W fan behaviour prevalent (who are posters in this same thread above me): I will illustarate in the following example-
"Cindy" pretends to like the rivals of her favorite skaters (in order to suck up to their fans in order to gain popularity for her favorite skaters): She gets a "following" of those other fans, such as "Billy" to like her favorite skater. "Billy" goes on fan gush of "Cindy"'s favorite skater. "Cindy" is happy now. Meanwhile, "Billy" is so enamoured he feels the need to every time please "Cindy", even if it means diminishing Billy's own personal favorites. If "Cindy" sees a poster, say "Sara" commenting harshly/critically on Cindy's favorite skater, she pulls out the iron fists. How so? By trashing Sara's favorites.
Those poeple ("Billy") are really not fans of their favorites as they keep hacking away that they are. If so, they would not feel needy to mutually suck up to "Cindy" every single time.
Again cyber politicking whatever you want to call it, nothing new in sports forums. For ex, Steffi Graf vs. Monica Seles: I was really disgusted by this fan propaganda on their tennis forums, when Seles suffered that assault Graf's fans did the exact same thing even 15 years later. It helps Graf fans feel I guess more secure, just like now, in that why not take an opportunity to promote your favorites now, its best possible time.
Is sad that "Cindy" feels bound to like/enjoy rivals of her favorite skaters in order for the rivals fans (like Billy) to in return, become fans of "Cindy"'s favorites. Normally it results in one thing: Sara comes along, criticizes harshly one of "Cindy"'s favorites in which "Cindy" finally lets loose. Wrath unleashed. "Cindy" could've unleashed her criticism of Sara's favorites long ago but chose not to in order to get Sara's following of Cindy's favorite skater. That is what I view as really unfortunate of "Cindy" as it exposes her agenda all along( and of course unsportsman like character too

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However, I am also getting the impression the real motivation behind these outrageous doom sayers is a few people's malicious propaganda, trying to damage these two's standing vis-a-vis Davis/White
Especially if such malicious proapaganda is instigated by person of authority figure.
But if "Cindy" has some kind of authority on the net many do not want to fight her on issues.