Are we really so sure that "fate" (if we want to talk with terms like this that I personally hate) is predictable? I doubt, honestly. And even if it were, does it always lead to the happiest possible ending? Not on this side of the Atlantic, though I must admit, judging from the reaction of the audience I saw the movie with, that many even here probably like to believe so, once in a while at least.
I mentioned earlier that you could sub out the words "fate" and "destiny" and "written" with "Faith in Jesus Christ Our Lord and Savior" and the film wouldn't suffer an iota. It has a ridiculously naive and filtered notion of higher power that is absolutely no different than the most easy and provincial faiths in this country that are so easy to mock. You see a little girl who says that she is going to heaven because she believes in Jesus Christ and it is no different in tone or content than anything in Slumdog Millionaire.
I asked my sister who loves it what the film is about. She said it's about overcoming all obstacles. I asked her if that means the theme is perseverance. She agreed. What does Slumdog Millionaire have to say about perseverance if "it is written?" If "it is destiny?" Nothing. You have an infallible protagonist who is going to win no matter what. The ending is an utterly botched conceit. He has no idea who the Third Musketeer is but there is little doubt of what is going to happen because it is written. The film has nothing to say about faith or the very notion of destiny, how it has become so ingrained in Jamal's head, or what it means to the Indian culture. The film begins on a title sequence telling us what is going to happen and the rest of the film exists within the confines of what I suppose the Zucker "Movie" label would call Underdog Movie. It has nothing to say about anything at all on the planet and I find its shortcomings in the most basic arenas of story structure to be astonishing.