I remember after the first mission on Venus where you first encounter and defeat the Vex you talk to the stranger and she mentions through the middle of the dialogue that "a side must be chosen even if it's the wrong side" that seems to me supportive of the theory that the traveler is not as pure as it seems to be. It could also be more expansive in its meaning that there may not be a "correct" alliance to choose. I personally think fallen, vex, hive, cabal, traveler, etc should not be trusted as humanity and or guardians in general are used as cattle or instruments to further these entities agendas which do not favor ours. Just my 2 cents