I don't think the Traveler is by any stretch what we would label as evil ... however, is it totally altruistic? Nope. It's a sentient being with its own agenda. That agenda may or may not align with what we consider "good." It gave us the golden age, but it was also ready to bail out on us when the darkness grew too strong and dangerous in our system. I'm certain this scenario had played out dozens or hundreds of times before after looking at the fragment lore. Rasputin stopped the Traveler, and in its damaged state it calculated that the ghosts were the best move for us ... and for its possible healing and redemption. TL; DR Traveler isn't evil, but might have something up its sleeve ...