Setting aside that it isn't quite true that anyone can sit down and read the Bible for themselves (many are still illiterate or barely literate in the world, and this was the normal condition of almost everyone just a short time ago), it's also worth mentioning that there are thousands of denominations specifically because texts aren't self-interpreting and every reader brings something with him to the table. Don't assume that because it seems clear that "the Bible says [x]" that that is really the end of the story, lest you trust yourself to perfectly understand God where billions of others have somehow failed. Humility is essential to the faith.