but in my country, the discussion does not even exist
Either you have a very enlightened population in your country, or you're making a big assumption about how everybody thinks in your country.
some people see SF as a genre to avoid or scorn, some people see other genres in that way too, but there is no question that it is a part of Literature, be it a good part or a bad part, that's a subjective individual opinion, but i never heard anyone say it's not literature, the full name for SF is Science Fiction Literature actually, and fantasy is Fantasy Literature.
Again, never heard is not the same thing as doesn't exist. The reason others may not follow what you are saying however, is that they believe that literature means good fiction only. So there's no "bad" literature in their view. Therefore if someone scorns SF as a whole (as opposed to an individual title,) they are saying that it isn't literature. It's bad trash. That's the literature-trash dichotomy for some people.
As for category markets, sure, they exist here too,
-- So you have category sections in your bookstores and specialty publishers and publishing imprints who publish nothing but SFF or mystery? Many countries don't have this, though they sell SFF, mystery, romance, etc., in the bookstores as fiction with other kinds of fiction.
I think it's wonderful if you do indeed have that, that genre is just part of the body of literature. There are countries where that is the dominant view and it's much saner. So why isn't it the dominant view, say, in the U.S.? Well, first off, in much of the populous, it is the dominant view, but there is also a class philosophy in the U.S. (and the U.K., etc.) that most people in the country are simplistic, low-brow morons. And so if you can argue that the majority of low-brow morons like something, you can argue that it can't be literary. (And this is often done by SFF fans as well.) And you can get such an argument into the media pretty regularly because they're lazy, and because it plays well.
There is also the use of literary as a marketing tool. This is why, even though books labeled literary are launched strategically and have about the same rate of success/failure as books that are not, the idea that literary books struggle to get anyone to read them at all while the barbarian hordes go only for brain-dead trash fiction is propagated because it helps sell the books labeled literary. They are the few, the elite, the last bastion of civilization, etc., so your reading club should read them and they should be adopted for college courses.
There is also the history of book publishing in the U.S. in which there were two book publishing industries in the 20th century, one which did mainly paperback and sold in drugstores, and the other which did mainly hardcover and sold in bookstores. And the two industries merged around World War II and post-war. And the social system changed. And non-white authors kept writing, and women kept writing. And all these things effect people's perceptions of fiction. And "genre" fiction, which was often put in paperback, which could be easily found in drugstores, which "common" people and young people read, which developed their own sections in the bookstore in the later half of the 20th century -- genre is a really easy target for those wanting to make imaginary wars, especially if you declare say the mystery genre to consist of thugs with guns and sex, or SFF as spaceships and elves with sex, and romance as cheesy melodrama with sex, and so on.
And yes, the Modernist movement certainly did have an impact on some people's perceptions, but the Modernist movement wasn't the only "literary" movement in the 20th century, nor even dominant. In fact, the Modernists were the young upstart revolutionaries for a couple decades. And now they're long gone, and some people may espouse their principles but numerous others don't. We have books that can be considered Modernist in every area of fiction and many that are not. All this clean split stuff Grossman was proposing as a way of discussing ideas -- the problem with that is people then think the clean split is fact, when it's not even close.
What separates fantasy and science fiction from other writing? What distinguishes it?
A good writer writes good books; a poor writer writes poor books. The category of book is immaterial.
There's your answer, from owlcroft. (Who then goes on to give what are owlcroft's criteria for a good book, with which others may or may not agree.) A fantasy book has fantastical elements in it. A science fiction story has science fiction elements in it. That is the only requirement. Everything else -- tone, language choice, style, plot, characters, what type of ending, etc. -- is not an attribute required for a book to be fantasy or SF, or a fantasy or SF title sold in the category market. You're trying to use Margaret Atwood's argument for why her book isn't SF, Bond. Fantasy is not a uniform movement like the Modernists. But the Modernists were a movement that
was part of the genre of contemporary fiction. The Modernists were considered a literary movement by some and commercial hackery by others. You can compare magic realism, a movement, against the Modernists, say -- that's two movements/styles. But comparing Modernists to the wide range of fantasy, which includes books that could be called Modernists, like New Weird? That requires you to try and stuff all of fantasy into a very narrow definition that is not accurate. Which Vandermeer was complaining about, and I'm always complaining about.
Why is it that The Matrix, Spider-Man 2, and The Dark Knight weren't even nominated for an Academy Award for Best Picture?
Why are there so few fantasy and science fiction movies nominated much less winners of the Best Picture Oscar?
Why is it that Seamus Heaney won the Whitbread and not J.K. Rowling when it seems he basically submitted a translation?
Because the people in charge of the votes or determining for those awards subjectively didn't think those things were good enough, and yes, many of them were probably fighting an imaginary culture war for those perceptions. Other people, however, put Neal Stephenson's Cryptonomicon on the long short list for the National Book Award. Other people gave the National Book Foundation's medal for distinguished contributions to American letters to Stephen King. (The NBF also gives out the National Book Awards.) Stephen Donaldson just got an honorary doctorate of letters from a U.K. university. And The Return of the King and Titanic both won Oscars for Best Picture. The other side of the imaginary culture war isn't uniform either.
How else do people determine what is taught in schools? Books aren't chosen at random.
They are chosen subjectively. Which is why numerous SFF authors like Ursula LeGuin, Peter Beagle, Stephen King, William Gibson, Ray Bradbury, etc. are studied in universities and also, pretty wide-spread now, in high schools. (Isaac Asimov used to complain of this regularly because teachers kept assigning his stuff to their classes and then students would contact him wanting to interview him and have him help them write their report on his works.) And there are also numerous people in education and academia who subjectively think this is bonkers. There is not a uniform view. As far as I'm aware, as well, the Victorian writers are studied just as much as the Modernist in universities. And other 20th century writers who weren't Modernists are studied too. You can't stuff all of them in one box anymore than they can stuff genre into all one box, Bond. Well, you can, but it's not accurate.
The culture wars, literary versus genre wars, etc. are all imaginary, but that doesn't mean that people don't keep fighting them anyway and that this fight over imaginary issues doesn't have an impact. But if you want to reduce this, I think trying to continue to fight the war that is imaginary, continue to use the old scripts, is not very effective. What has been working a lot better is just to say that the war is imaginary and inaccurate and then talk about the books as individual books. That doesn't mean that we don't have a fantasy genre/category market anymore. It's just that we don't define it as a narrow style, but instead a type of fiction that is infinitely varied.
There are a lot of critics who are doing this. There are a lot of authors who are being sold this way -- in fact, it's the norm now for SFF. And it's helpful not just for genre writers but particularly for women and non-white writers, over whom these types of perception wars are also fought.
I understand what you are saying about the perception of us Yanks being stupid through our tabloids, etc. 
