Well if you want to use the "It's in the game" argument then let's all play a free for all with items on and play on hyrule temple! It is a part of the game, right?Is he in the game, or not? Discussion closed.
My point here is that tournament are about finding the most skilled player. Things like items and dumb stages take away the skill required to win and turn the game more luck based and more of who can out-gay the other person. When something in the game is unfair or broken, like things such as items, stupid stages, and metaknight, tournaments take it out so that the game is fair and can determine who is the best player.