This evening, I had occasion to comment on a question that concerned in part a simple disagreement in number. The moderators, for unknown reasons, deleted several useful and instructive comments of mine which pointed out that, although native speakers in everyday discourse often, and to no ill effect, play fast and loose with agreement in number, the "correct" form of such a sentence (and the word "correct" was enclosed in quotation marks, so that no-one could possibly mistake my meaning) holds that subject and predicate should agree in number. The OP, evidently, clearly understood, and even expressed his gratitude for this comment! Yet it was deleted, along with my subsequent attempts to provide it again.
When a useful answer to the question was then posted, I commented there that, since the underlying structures of Chinese and English have nothing in common, it might be wise to consider abandoning any attempt to find similarities in the grammars of the two languages, and instead to "start from scratch". (This is hardly a remarkable observation.) This comment too was deleted! It was:
This is an interesting answer, but it is important to point out that Chinese and English are completely different where the concept of "grammar" is concerned. It is often and truly said that Chinese has no 'grammar', and there is wisdom in that observation. The Chinese learner of English is well advised to abandon any attempt to understand English from the perspective of Chinese language structures, and instead to "start from scratch."
In the midst of this, a common troll, new to the site, posted standard "challenges" to my comments. I dismissed the troll's barefaced attempt at disruption...dismissively. Even though it was obvious from their tone and wording that my comments on the question were intended not as prescriptivist claptrap, but to inform the OP of what is expected in "correct" usage, every single one of my earlier comments was also then deleted!
What reasoning underlay these deletions? Are the progress and understanding of the questioners here not our primary concern? I fail to see how it is better that a new learner of English not understand what is meant by "correct" as it pertains to simple things like agreement in number. An understanding of vernacular speech is good, but it ought to rest on a foundation of what is considered "correct".