Quintus finds it really unfortunate that Terezi chose the side she's on. I don't think he entirely recognizes it as such, but she's rather like him in a way--someone who both cares and is a little too smart for the slot the Capitol was willing to stick them in. He enjoyed being able to talk to her on a human level and her kindness, as small a thing as it was, does tug at the heartstrings of a guy who's spent most of his career dealing with belligerent citizenry and incompetent colleagues. In war, it's easier to be able to demonize enemies, but in spite of her defection, he has a feeling that she isn't liable to reduce him to his title--and in turn, he isn't going to quite be able to see her purely an agent of trouble, either.