Picking up on Glen's thinking about the Sopranos' moral universe, I'd say that the writers are depicting what love, passion, and desire look like in a climate of (largely) unfettered greed, corruption, and amorality. Yes, this is the world of organized crime, but some theorists would say that the potential for similar urges, if not actions, exists in us all. These theorists might point backward in the life cycle toward a time prior to the establishment of care and concern for others, when the infant (presumably) wants what it wants and harbors fantasies of destroying anything or anyone that prevents it from being gratified instantaneously. Ralphie—the king of narcissistic sociopathy—wants a luxurious bath rather than hanging out with (and supervising) the son he rarely sees. (We might ask, was there an unconscious wish for the kid's death, letting him play with a sharp bow and arrow?) Tony has stolen Ralphie's ex-mistress and expects nothing but acceptance from Ralphie (though when the shoe was on the other foot, whipping was in order). Ralphie exacts revenge (as I see it) by destroying the "other" stolen love object Tony took from him—his horse. And Tony then destroys—and destroys and destroys—Ralphie. Primitive desire, which when thwarted leads to primitive revenge.
The power in this portrayal lies in the way it shows us the underside of desire and passion, the "heart of darkness" that in subtler, less egregious forms may be part of the human psyche. What makes this depiction less tragic (as it is in Shakespeare) than revolting is the complete absence of forethought, afterthought, or remorse that we see an any of the Sopranos characters after they've let loose. Is that just them, or is the capacity for such frigid detachment to be found within us all?
By the way, anyone see any benefits of therapy here? Looks like the writers have definitely given up on Jennifer and on psychoanalytic treatment, if not on human nature itself.