So I guess you don't believe that art is anything other than entertainment? Or that an artist's creation isn't their own, but somehow turns into pop culture? Sure, there are many interpretations of Starry Night or Beethoven's 9th, but there is only one "true" (or canonical) Starry Night or Beethoven's 9th. It doesn't make later interpretations un-entertaining or not worthy of our enjoyment, but it isn't the same thing as the original.
For example, we have
this and then we have
this. Both are great, but the former is the "canonical" version of Blue Monday.
Note also that Lucas, Greenwood, etc licensed those properties out to be further developed. Tolkien didn't. Even if the Tolkien estate licenses someone to write a sequel, it will never be "canon" - just some authors story that uses words and ideas from Tolkien.
So for me, there is Tolkien and then there are interpretations of Tolkien - that includes Bakshi, Jackson, and the Rings of Power. They aren't the same. To use Tolkien's terminology, if his Middle-earth is a "secondary world," all further interpretations are "tertiary worlds" (a term he didn't use, but I think it works for this context).
p.s. Re: sacrilegious. I wouldn't get too hung up on the word - I don't mean it in a religious sense, but more in terms of artistic fidelity. But if you can't separate that word from its religious context, replace it with "dishonoring" or "disrespectful" - that is, of the artist's creation.