It’s a threat, not a fallacy. And if I understand LW correctly, few would notice random want-ads because they wouldn’t gain enough votes to make it to the front page.
I’m pretty sure the problem is EY. He could post pictures of his cat, and they’d go all the way up. (And if he doesn’t have a cat, then he should know that there are several in my neighborhood who might be happy to be adopted. And kittens! Omygosh!)
Require new top-level posts to use a tag that indicates which facet of LW’s interest it lies with. So each new post would have to choose on (or maybe more) of tags like “bayes”, “selfimprovement”, “philosophy”. So, if I think that Lesswrong should really dedicate itself to the study of Victory and nothing else, I might read only posts with selfimprovement tags.