Poor analogy, IMO. A manga is what it is, take it or leave it, but we have power over the comments and community here. And comments can have utility: adding cultural context, clarifying obscure points, pointing out things people missed. All of which are made more painful if you have to wade through a sea of self-indulgent negativity.
And defining any negativity as “self-indulgent” is itself quite counter-productive; I’m not sure how much more “self-indulgent” than Eroswhite’s “positive” rant a post can get.
A lot of readers have been following Citrus for nearly a decade, many of whom, like me, thought highly of the series at first, and while many of the vocal critics have been disappointed with the quality of its long-term execution, they’re still interested enough to follow the story and its characters and to find occasional pleasures along the way. Telling those readers, many of whom also do the positive things you list above, to just shut up and go away isn’t going to work.
The “If you don’t like it don’t read it” argument certainly does cut both ways, and critical readers with a long-term investment in a series have just as much right to comment as those who are happy with it (assuming “Yes Mei has been shit” counts as “happy with it”).
