Eco himself distinguishes between "light fiction" and "literature", and I've seen countless articles on the dissatisfaction that authors feel when their works are labeled as works of a particular genre. If the case were as clear as you claim, I doubt that would happen. Labels only hurt when they stigmatise (one of the reasons "cracker" never took off, by the way), and the label of "fantasy" or "sci-fi" certainly stings.

The reason, as I stated, is that the genre label is a way of tipping off the would-be reader to the formulaic and derivative nature that the reader is presumably looking for. An author that seeks to write something meaningful and thought-provoking would not like to be seen as formulaic and derivative. Hence, "genre" has become synonymous with "derivative" and "light fiction".

Also, for the record, everyone is ultimately a dilettante when it comes to literature - and not only because most of the English majors are cooking their latest batch of French fries at McDonald's. An English degree (or literature degree) is by itself worthless. I should know this, because I'm actually not a dilettante. I have a degree in Russian Literature, in case you've forgotten.

I find your use of academic catchphrases that really say very little quite funny:

Rather, the trend seems to be going toward recognizing that there are literatures of the mimetic and the speculative that co-exist simultaneously in various genre typologies and that analysis of these literatures has to take on a multi-pronged, more inclusive approach than had been previously the case.

You could have simply said "Consensus is that a speculative genre shouldn't be used as a criterion for excluding a book from the definition of literature". The Economist Style Guide would be the first to tell you to tone down the language to see you haven't said much, could have said it more elegantly and more simply.

If only someone had told Dumas the same thing...