Why is shadow the hedgehog so mean

Shadow'spessimistic sarcastic and generally moody personality can be traced back to his formulative days on-board the Space Colony ARK, where he witnessed the death of his closest friend and his creator's dissent into madness. Shadow spent the early part of his life on the ARK, where he quickly got to know his creator, Prof. Gerald Robotnik and his twelve-year-old granddaughter, and cousin of Doctor Eggman, Maria Robotnik. The United Federation's army grew nervous of the power possessed by Robotnik, calling for a mass genocide of all the personnel on board the ARK. This resulted in Maria being shot at a close range by a soldier. She was able to live long enough to capture Shadow in a glass cylinder, which was then fired at Earth, saving him, but dooming Maria. Without medical attention, she died soon after. In flashbacks before this event, shadow is seen to be a philosophical figure, very reserved but pleasant. He shares many a discussion with Maria over what Earth is like, never showing any sign of disgust or sarcasm. However, once he was transported down to the planet, it removed him from Maria, who was like a sister to him. The knowledge that he had allowed his greatest friend to die did terrible things to his mind, along with tampering to his memory that the professor was somehow able to do. This all culminated in a darker, more vengeful Shadow rising from his slumber fifty years later. He looked down upon humanity and those who were around him, which was not helped by Eggman's expectation's of him being a super weapon, his own internal conflict and Sonic's accusations of Shadow's inferiority and him being 'an impostor' Eventually, he saved the planet from a destruction that Robotnik planned for it, but fell back to Earth and lost all of his memories. He remained a depressed and misunderstood creature until one day his biological father arrived on Earth, an alien called Black Doom. He was confronted both by Doom's forces and from the military, GUN. These only served to make him more violent, as GUN treated him as a weapon and Doom urged his destructive personality. This ended when he finally regained his full memory. This once again made him slightly more intellectual, yet he still had grudges against Sonic and his friends, resulting in a slightly darker version of his first state of mind.