This isn't a theory, more like just something to think about. I know the traveler came and gave us the golden age and all but remember that the darkness has a vendetta against the traveler not the humans specifically, meaning if the traveler had never came to us, we would have never had the golden age but at the same time we would not have been reduced to a single city by the Darkness. And on a side note, most people don't trust the speaker (I don't either because he is shady as hell) but don't look at him for a big plot twist because that would be to easy and we all know Bungie knows how to make an incredible story. Just some things to think about.