I agree with leaving things out and moving events from one “book” to another in order to make an effect film. I even agree with depicting events on screen that were described in conversation in a book. In a book, words are words, whether they’re “live action” or a conversation, while on screen, fighting (for example) is not at all same as talking about fighting.
However, making up new material - action that didn’t happen in the book, stupid modern jokes, significant changes in characters - is inexcusable, in my opinion. It’s the imposition of the filmmaker’s ego over the author, just because he can, and I believe it is dishonorable.
I saw the old, animated “Hobbit” movie when I was a child. It may have inspired me to pick up the book, but it was so long ago that I don’t remember.
Some of those really bug me too. The little things like stupid jokes more than the big things like character changes, honestly. I adore LotR; it’s been a favorite since childhood. But there’s very little character development. It’s essentially a milieu story. That sort of works in a book but it really doesn’t work in a movie. Movies need to be character or event driven. So in order to make the movie work, they inserted character changes.
I don’t like a lot of those changes. Aragorn’s particularly bug me. But it did give Aragorn growth as a character. He had goals and fears. Original book-version Aragorn... didn’t.
Some of it’s hubris, the filmmaker thinking he can tell a story better than the author. Some of it is translation difficulties. And we as viewers have to decide how much altering of the source material we can take. There will always be some. I know exactly how Smaug looks and sounds and the movie version will be wrong, guaranteed, but I expect to enjoy the movie anyway.