Actually, if you watched the Game Theorists video, it states a clear solid theory of why the Traveler is evil. For one: A clip of a player playing a mission on the Earth shows a Fallen Dreg fleeing from the player, shouting a very distinct word: "Darkness" The Fallen Dreg shouted the word until the Fallen was killed, which sparked some uncertainty. Secondly, A Grimoire card shows a Guardian Hunter entering the Gardens and reaching for a Ghost-shaped flower. WHen the flower pricked him and drew blood, the Ghost said "This is a place of life. You are the Darkness, an undying evil" (not the qutoes but close enough) The hand drew blood from the puncture wound and hasn't healed since the Guardian left the Garden. During the Beta playing, one of the few players who tested it spilled the beans. The player stated that the Traveler was portrayed to be a figure you could not trust. Zavalla, and the other Vanguard give the Traveler out to be a selfish machine that doesn't want help but is out for its own interests. Shortly thereafter, the game was changed to portray the Traveler as a etheral God of some sort that saved the Universe. Bungie as said earlier, changed the minor points of the storyline due to the leaked gameplay and evidence. I mean, who would want to spoi the surprise. There is a full theory on the Game Theorists channel, so be sure to check it out at the link below: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwijutjR3fLKAhUCKB4KHZcXDW0QyCkIIDAA&url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DY5NbEjkkPlI&usg=AFQjCNEpimTdxUaymGoJgQ78OJiB_9P2IQ&bvm=bv.114195076,d.dmo