There's a lot pointing to the Traveler not being the entirely benevolent god it's made out to be. People with indications of brainwashing after first sighting it on Mars, the fact that all signs point to the Eliksni (now known as the Fallen) having been the Traveler's chosen at one point in some form, then abandoned. Also, the fact that the damn thing leaves ruin in its wake. The Fallen lost their homeworld, then subsequently their entire species identity. There's some evidence that the Cabal are only running from the Darkness because the Traveler passed through their system and led the Darkness through their worlds by result. There's also the fact that, while running from this, it immediately began rapidly raising the tech level of the native species (us) at an alarming rate. We're not being saved, we're being used as an army to protect it. The Ghosts and Guardians are just an extreme measure of this because it's helpless right now. I don't know if it's evil or not, but the Traveler is at best ruthless and careless. EDIT: Oh! And go find the Taken King inrto cinematic with Ghost narrating and rewatch it. Nearly every planet and moon the Traveler passes by explodes.