How cognitive science explain the stylistic convention in text writing? Some researchers and writers published books about this topic: how the psychology influence the taste of the readers.

It's very intuitive that the word choice matters when we want to be persuasive, capture the listener's attention or simply avoid to hurt him. The importance of the presentation is clear to the human kind since thousand of years, but only with the psychological studies we have clearer some influences of a speech which are counterintuitive.

To better clarify the topic: trying to help someone may hurt his self-esteem if he interpret our attempt like a statement of superiority. 

Now I was looking at this revision, which I put also here for easyness: https://academia.stackexchange.com/posts/29363/revisions



The last part which was deleted contained an opinion which was slightly critical. Another user deleted it. We may some reasons to agree with his behavior but this is the point. Why do we agree on his revision? Why human being living in different countries developed the same beliefs about focusing the discussion on xxx and rejecting yyy.

Pscychology somehow teached us that beliefs are not absolute as everyone would think of his one. So, if every convention was caused by something. The convention related to the definition of rethoric and dialectic should be deep into the human brain structure.

NLP is not a science, however are there serious books to study about communication seen in a scientific way? 

Why are that kind of sentences (the one expressing polemical opinions) rejected by most of people?
I don't think there is a stylistic convention in text writing that prevent the expression of an opinion. There are countless texts expressing a subjective view or controversial points. The example you picked up is somehow very specific to academia.stackexchange.com. 

The website explicitly tries to prevent the expression of an opinion - see https://academia.stackexchange.com/help/dont-ask about the possible reasons for a question to be flagged (and removed) as primarily opinion-based - e.g. a rant in disguise. This rule echoes the way science is made of - facts and interpretation -, especially in its formal way of communication. Researchers sometimes express an opinion in an article but it is usually advertised as such - see the specific section called "opinions" in the journal Trends in Cognitive Science for example. 

In the case of the removed sentence, I guess that the reviewer relied on "I would prefer" and "my opinion" to build his/her opinion.