Actually if you read some of the calcified fragments from the taken king,you learn that the hive was visited by a light,a god that gave them power and then killed them off and made them what they are now. Likewise the same is for the fallen,a god visited them which is why their primes look like the traveler. Also its even been said that the traveler has visited other races,and all of them have fallen to the "darkness" it is why their powers and various other things are similar to us,likewise its why the reef doesn't trust us or why there are dark guardians that do not embrace the traveler. It is evil,it has brought the downfall of many.and will do so to us,its a game between it and this darkness,we are nothing but pawns to it.