The Book of Sorrows is clear that they have familial attachments even if their concept of love, joy, etc are warped. They even had compassion/guilt originally in their whole mass slaughter thing. I mean he straight up says he should have some kids so he can both love and kill them. And Oryx straight up screams "Vengeance for Crota!" and "I will have vengeance!" at you in game. Everything in the TTK story points to Oryx having a personal beef with you over the death of Crota. Near every NPC says it at least once. All the marketing says it. The trailers say it. The commercials say it. Bungie said it. Its pretty silly to say otherwise. -.-