Acctually I very good theory on why Xur hates warlocks. Upon his first time showing up to the tower. Ikora rey was sent to see to his need. She saw him and said what are you and had a group of warlocks detain him. They had brought him to a closed off room and had almost dissected him. Luckily Cayde and Zavala had heard that the group of warlocks had detained him on Ikora's orders. So Cayde and Zavala ran as fast as they could to stop Ikora from murdering Xur. And Xur now hates all warlocks while he gives out all the Hunters and Titans the good exotics as thanks. What do you think?