First, bravo for taking on a controversial subject!

I think your conclusions about Tolkien's Christianity are wrong. My reading of Carpenter and other sources tells me the opposite: I believe he was a Christian. But he was also a scholar, and a man who was deeply against the use of allegory in fiction.

The only way for a Christian to write an epic fantasy acceptable to Evangelicals is to write an allegory...and LOTR is not that. Allegorical fiction was C.S. Lewis's thing, and as much as Lewis and Tolkien liked each other, Tolkien was not a fan of the Narnia books.

Speaking of Lewis, per every biography of Lewis I've ever read it was Tolkien who convinced Lewis that God was real and Christianity was a philosophically valid belief system. Pretty tough work for someone who doesn't believe it himself!

Your view of how Evangelicals read books is, I think, spot on, as is your conclusion that Tolkien was a religiously disruptive writer. All great art is disruptive. And, of course, no matter what the evangelicals would like to think about Tolkien and his work, by definition he wasn't one of them (neither was Lewis, come to think of it, though you'd never know it the way he's come to be worshipped). One of the problems of believing one possesses the one true faith is that all others are diminished, unworthy.

LOTR is a book that speaks to truths that are much broader than mere religion. I believe it is a work informed by Tolkien's Christian view of the world, though not overtly Christian. By creating a world without religion, LOTR becomes a story that transcends religious differences. I think that's all it needs to be.