Phillipa Boyens (one of the writers of the Peter Jackson Tolkien Adaptions) made the comment that a Tolkien Purist is some one who is a self proclaimed guardian of the material.. I would argue that a Purist is a person who simply doesn't like her monkeying with the material... for her own shallow social engineering/politically correct reasons.
Don't get me wrong, I realize that certain changes must be made to adapt any novel to film or television. For the most part the changes to the Rings films were mild. This isn't some rant about Tom Bombadil being left out. The films also could have been much worse, after all the Hollywood financiers wanted them to kill one of the Hobbits! Make no mistake, bullets were dodged. But it was clearly the screenwriters choice to so drastically alter the entirety of Faramir's character. It was their choice to alter Theoden's character. It's there choice to add characters when they don't really need to be added. All of these things can and should be laid at their feet.