Two out of four questions I asked previously on this site have been closed: one pertaining to the order of words in a particular context; the other about the meaning of the expression 'chorus line'
Actually, four of the seven questions you have asked have been closed. More on that later.
...the other about the meaning of the expression 'chorus line' — a piece of info not available in the dictionnaries [sic] I looked up in the first place.
By reading the question, there is no way to know that you looked up the word in a dictionary – that was a key reason for the closure of that question.
I am amazed, because several users took the pains to answer both of them and vote me up while I was grateful for what I considered valuable help.
You have one upvote on the chorus line and one answer; that's hardly an outpouring of support for an excellent question.
This forum sports a vote-down mechanism as well as a vote-up one
That's true; ELL has those mechanisms, as well as every other site on the Stack Exchange.
...and I see no reason why users should be deprived of the right to decide for themselves and subdued to arbitrary or over-subtle arguments by allmighty [sic] 'bosses'.
No, people don't have the right to ask anything they want on a Stack Exchange site. The Stack Exchange is made up of dozens of sites, devoted to topics such as Technology, Language, Theology, Gaming, Science, and Art. Every one of these sites is designed with guidance about what is considered on- or off-topic, and users with sufficient reputation are encouraged to help keep the site free from substandard and off-topic questions by using mechanisms such as downvoting, close voting, and commenting.
It's also worth noting that the site puts closed questions in an "On Hold" status, designed to give the original poster a chance to revise the question, so that it can meet community standards and be subsequently reopened. As of this writing, you've had nearly a month to improve your question, yet it remains unedited and unimproved.
I am now in an utterly absurd stance: while gaining credit from users, I am being discredited by some overpowered oligarchs and, to add insult to injury, I am being menaced: upon posting a new question this morning I was warned (?) in colour red that I might me barred from the forum should I ever dare ask more irrelevant questions of the kind.
Unnecessarily colorful language aside, I believe the "menacing" you allude to was an auto-generated warning. I'm not sure about the algorithm that gets used, but, however it works, it was designed to exhort you to increase the quality of your questions. (Evidently, four closed questions out of a mere seven asked is enough to get the attention of the software.)
If you want to learn more about how all this works, I suggest reading through the following questions and answers on Meta Stack Overflow.
(I especially recommend reading Jack Maney's answer on that last one; it has a lot of interesting information and discussion.)
Understandably I am not a native English-speaker. If the high-ups here think this forum a place reserved for English native-speaking PhDs in linguistics, let them advise it clearly on the home page: I will split and quite naturally let the Internet World know this is not the right place for the benighted to show up.
I'll say it again: chill out. Asking a user to show us what they found in the dictionary when asking a "what does this mean?" question hardly amounts to requiring a PhD in linguistics.
You should try interpreting the feedback you receive as the helpful advice it is intended to be, rather than as the personal slights you've perceived them to be. The sooner you learn to do that, the quicker you will see ELL as the welcoming and helpful place that it is.
Good answers take time to write, and there's little value wasting other people's time simply because you don't want to take the time to learn the proper way to ask a question.