Harry Potter?

So, I was watching t.v. today and I see the trailer for the new Harry Potter movie: The Order Of The Phoenix. There was one scene where Harry was fighting Voldemort and I'm thinking, okay, here's a chance for Harry to use his awesome unforgivable curses, I mean when fighting Lord Voldemort, there should be some kind of exception to the law where if you use one of these curses, your magical powers get revoked or something. So, Harry, being the intelligent wizard that he is, uses... expeliarmus! A pathetic little spell that he learned in first year. Seriously, he could have obliterated Voldemort with the Cruciatus Curse, the Imperius Curse or Avada Kedavra, but instead he uses expeliarmus. Honestly though, he spent how many years at Hogwarts breaking like every rule possible yet when he has a chance to break just one more rule in exchange for banashing "You know who" he suddenly turns into Mr. perfect student .He should be banashed as a wizard for not using an unforgivable curse...

This talk of unforgivable curses reminds me, why are there unforgivable curses in the first place? Ah well, don't question the almighty witches and wizards Seth. Oh by the way.... SNAPE KILLS DUMBLEDORT (in the new book). Hehe.