Emotional subjectivism makes us susceptible to the suggestion that whatever is connected with 'genuine emotion', whatever must be recognized as 'authentic' in its emotional content, is good. Hence the temptation to reduce love to nothing more than subjective emotional states. If we do this, love finds its whole content and sole criterion in emotion. The affirmation of the value of the person, the aspiration to the person's true good, to union in a common true good -- none of these things exist for a will subjectivistically fixed upon emotion as such. In these circumstances sin arises from the fact that a human being does not wish to subordinate emotion to the person and to love, but on the contrary to subordinate the person and love to emotion.
[Karol Wojtyla, Love and Responsibility, Willetts, tr. Ignatius Press (San Francisco: 1993) p. 163.]