I have read the entire series (Hobbit + Lord of the Rings + Silmarillion + Children of Hurin + Tales from the Perilous Realm) less the books of notes; and, had I the time again, I should fling them all on a pyre and say the Little Office of Our Lady several times in the wasted time.
Firstly, I regard fantasy literature as essentially sinful, the equivalent in our times of the chivalric nonsense that Ignαzιo de Loyola stuffed his head with before becoming St Ignatius. Has not Holy Church a hundredfold more pure, real wonders than the vanities of a corrupted mind? Let us use our time in sincere prayer and loathing of our rotten flesh.
There is at least one case of impurity (the dwarf Gimli's ''courtly love'', or syruped and begowned adulterous lust, for a married woman, presented entirely positively, indeed praised), indeed these fester through Mediaeval writings and Wagner's operas. The Children of Hurin has a case of (admittedly accidental) incest uncondemned. Such filth ought never be mentioned: have we not the Lives of the Saints to read?
The cosmology of the Silmarillion is essentially Gnostic; and it is worth pointing out that the contradictory accounts of the dwarves and elves are given without condemnation of one or the other, a grave relativism.
Taints of paganism are present too, Gandalf described as an 'Odinic wanderer'', ''dwarves'' and ''elves'', which are essentially wicked and pagan, regarded positively. His Modernistic ideas on myth and his distaste for allegory, long used by the Church Fathers, both were used in an article I once read to make a case he was a Gnostic.
His presentation of Purgatory (implied) in ''Leaf by Niggle'' is essentially humanistic, a more or less pleasant time of self-knowing and hard labour, not the blazing agony that awaits us poor vermin for our sins -- as we richly deserve.
I have never seen a revolutionary or other enemy of Christ make good use of an untainted work. The Breviary has never inspired a sordid fantasy novel! Thus, I regard it as deeply tainted and to be avoided.