I finally had a chance to check it out. At first the woman in the show starts listening to Chopin (previously outside of her ken) and finds it makes her more irritable with her boyfriend; the woman's mentor (who had originally recommended the Chopin) says it can "stir up some dust." But then in the end, she gains self knowledge, and it becomes clear to her that she wants a man-upgrade: "Sometimes the truth speaks from a peaceful place." And this music brings you there.
The initial introduction of Chopin's music in this episode was unfortunately a use of the "classical music is for psychos" meme, which Alex Ross discusses in "The Rest is Noise"--an association stemming from Wagner and the Nazis. The butcher's crimes in this show were described as elegant and flowing and disciplined and exact, therefore like Chopin's music. Completely backwards. But that is the rigid meme of our backward culture in which "wicked" is good or funny and wholesome is "boring" and "suspicious."
In fact, the criminal mind is a disintegrating machine, not a harmony- or closure- or clarity- or catharsis-generating integrator. The criminal's natural "music" is chaos, mayhem and destruction, just as it was in the Weimar culture of Germany before the Nazi's came to power. Think Schoenberg and the original, creepy version of "Mack the Knife." Chopin's ethos, on the other hand, is that of the Enlightenment, the age of freedom and mutual respect, clarity and self-knowledge, and self-integration.
A significant factor behind the reversal of value-judgments is the morality of self-sacrifice. If the good is (per altruism) inherently painful to the self, and the bad (pleasure, selfishness, etc.) feels good but in some guilty or corrupt way, then the evaluations are all set in reverse. What is good for you (self-integration) must be perverse and abnormal. What is bad for you (chaos and mayhem) must really be "liberation" and the only kind of "selfish freedom" and "pleasure" possible given the metaphysical assumption. This is the kind of thing we get in the bizarre cultural soup we have today, subjectivism plus sacrificial/backwards morality. The morality of self-fulfillment rectifies this, but most people are on the opposite premise.
FYI, the show Dexter, overall, seems like a large study in the manipulative traits of "cluster b" personality disorders--something very needed today from the point of view of education and common knowledge.