The stuff in your spoiler tags was completely based on speculation. In the game, he had not mentioned ONCE that he knew who his real mother was, and your argument in there isn't really that good. I can't really take it apart, becuase it's all based on speculation, and what you think.
Also, it wasn't the fact that he killed the Midgar Zolem, it's the face the it was "impaled" on a tree. Just look at it... It's like, art. The style was simply cold and incredible.