It's ridiculous as in "worthy of ridicule".
In the canon Sauron is very clearly depicted as a sadist and Mordor as a kingdom which very deliberately loathes and destroys beauty.
You can simply choose to ignore all of that, so that Mordor is beautiful and free and happy , instead of sadistically destroying beauty, freedom, and happiness. And you can likewise choose to ignore the technical achievements of the Numenoreans and the Dwarves, the poetry and philosophy of the Elves, and so forth; the ways that every civilization in Middle Earth had beauty and music and philosophy EXCEPT Mordor. You can choose to deliberately reverse all that.
But then you're no longer doing anything that comments on Tolkien's actual work --- and to claim you do is ridiculous. i.e. worthy of ridicule.
So, as lucidfox said, this is ridiculous - not rationalist, but just revisionist.
But then you're no longer doing anything that comments on Tolkien's actual work
It looks like it's basically shifting the view of the original LotR into an in-universe text with some serious history-as-written-by-the-winners bias instead of objectively described stuff that really happens. Haven't read the book yet, but this seems like a pretty interesting approach to me. It's a fun twist on the generally very literal-minded way speculative fiction is read.
This may be old news to some people, especially the Russian speakers, but I didn't see an article about it here.
In 1999, Kirill Yeskov, a Russian paleontologist, wrote The Last Ringbearer, a 270-page take on Lord of the Rings from the point of view of a medic in Mordor's dying armies who is also a "skeptic and a rationalist." In fact, Mordor represents the forces of reason in this retelling of the story. As a Nazgúl (himself a former mathematician) explains, Mordor is "the little oasis of Reason in which your light-minded civilization had so comfortably nestled." Barad-dur is "that amazing city of alchemists and poets, mechanics and astronomers, philosophers and physicians, the heart of the only civilization in Middle-earth to bet on rational knowledge and bravely pitch its barely adolescent technology against ancient magic."
The story has been newly translated and is available in free PDF form -- in English and the original Russian. There's a recent review from Salon as well.