Here's the interesting thing about a fiction: it only works if it gives off the illusion of fact. The worlds fiction creates have to look or seem real, and the characters and situations have to strike us as human and plausible, even in the wildest fiction.
In a similar way, subjective moralizing only works because it assumes the mantle of objective morality. It pretends to be a "morality," in other words, and pretends to have value in delivering the goods we always look for in objective morality. It pretends it can make us "good people," or "principled" or "decent." It pretends it can inform an agreement, a polity or a civilization. It pretends its delivering real moral information to us. But all the while, it delivers none of these things.
It's pure self-will dressed up in the borrowed robes of moral rectitude. It makes us think we're "good" for only being impulsive and self-centred. Yet, if imitation is the sincerest form of flattery, and if, as is the case fiction offers tribute to the reality of fact, subjective moralizing kneels as the feet of objective morality, without which subjectivity would be able to achieve no moral sheen at all, and would be seen for the empty fiction it really is.
