@RobertLongson, Is it better now?

It's part of what we do, keep watch on the quality of answers. Ones not supported by credible sources get comments, downvotes and are either edited, or deleted. Often answers will disagree, or make reference to different models describing the same complexity but from a different point of view - but that's part of the way science works anyhow, competing ideas and testing them. Without reference to specific questions or answers this seems impossible to give any more of a detailed answer than that.

@W.O., but sometimes (like here), questions are highly downvoted (and, sometimes, closed later), even though they are useful (or at least good)

That's not a science site, the rules on English Language Learners and what's on topic are something you should check-out in their help centre. It's not clear what answer you might be referring to, the one you gave is unsupported by references and seems to be purely opinion-based. If you've a specific question for their meta then please ask it there.

@W.O., I'm asking why did the rules made people downvote and, later, close my seemingly useful question?

It's off-topic for that site. You need to read the help centre of any site you post on to ensure that your question is on-topic before posting it.

@W.O., please consider enhancing your comment to an answer, and include a link to where anyone can find the rules that apply to Stack Exchange Network as a whole.

There's the FAQ and the per-site help centres for you.

@W.O., what is the difference between FAQ and Help Centre?

We've given you enough to go on, you are expected to do some of the work yourself. Try reading the FAQ and the help centres, you'll see the difference.

@W.O., "It's part of what we do...", Include this text or an improved version of it as an answer.

I've cancelled my duplicate vote a while ago as I made it in error. I'll leave it to others to answer or decide otherwise.

@W.O., May I ask why could this question be considered otherwise if it includes a question that is not explicitly asked anywhere on Meta Stack Exchange? I want to understand, not against that.

To be answered, you'd need to provide a metric by which reliability can be judged. Asking on a website or network of websites how reliable they are is naïve as it supposes that you'll get a "reliable" answer - it's like asking a snake-oil salesman if they're trustworthy. Nullius in verba - a saying meaning "take no-one's word for it" would seem to apply, i.e. you need to learn to judge for yourself each occasion on it's own merit, each answer for it's validity.

You seem to be asking a question about basic epistemics, which is more suited to philosophy than main meta - and it's something unlikely to appear in the help centre. It should be taught in schools as mandatory in my view.

@W.O., I am asking about how reliable do experienced users of this website find it, I am not asking the owner. The same concern is also answered on Wikipedia for example.

Very. Or not at all, or a bit on Thursday afternoons, but don't ask on Mondays unless you want silly answers. It is Monday today - that statement is totally reliable. ***** As I stated, you need to learn to judge for yourself. Else go find a fact-checking service that rates sites by reliability and look-up ours. That's if you can find a reliable fact checking service.

Part of the problem here is that you're asking a broad, open-ended question soliciting opinions - that is absolutely not what we do here.