seems to fly in the face of J.R.R.'s intentions so far as I can discern themgiven that he sold the rights to filmmaking for dirt cheap and also that he supposedly wanted to encourage the creation of a broad culture of myth, folklore, music, etc from fans)

Not so at all. For all the popularity of the 'other hands' quotation, which the elderly Tolkien used to describe his youthful ideals decades before, in real life JRRT was fiercely protective of his copyrights, and detested 'fanfic.' NB: it turns out the old Professor held out for a better movie deal than anybody knew- and only did so because (1) he was confronted with a huge tax bill, w/o ready cash, and (2) he was convinced that the movie couldn't possibly be made, at least in hid lifetime (correctly)  .