I think the traveler is a fleeing angel. The light is good/beneficial to humanity and similar races, the dark is bad, but the Traveler is not light itself, it is a source. (My source for this is that our enemies wield different light burns) I suppose the Traveler originally was benevolent to humanity, but it went from a free service to a paid service pretty quick, it needed golden age humanity to protect it. Now it still helps us, but it also seems to have caused our collapse. So, in the end I say it's good, but it's screwed up humanity's evolution in every way imaginable lol. I also doubt the vex have any way of stopping the traveler without the aid of darkness, considering the traveler smashed them at some point.