The Traveler left the Fallen because the Hive were chasing it. It decided to stay here and fight. That is simply a belief in the nature of the Traveler and the Darkness, as are all the other explanations on that card. The card simply calls Guardians "dead things made by a dead power in the shape of the dead. All you will ever do is kill," This is true: we're corpses reanimated by a crippled and dying power to protect humanity. Of course we're going to kill. The "Traveler is evil" storyline was scrapped along with most of the original story.