"I could care less" reminds the listener of your human compassion as an American. You are essentially telling him or her, "as you can tell from my clearly stated opinion, I do not care very much at all about this subject I am referring to. However, let us never forget that--if I wanted to--I could care even less." As we are sometimes prone to speak in hyperbole, e.g. "people who park crooked like that should be disembowelled and set on fire" (when a jail term would obviously suffice, given the spectre of rape), "I could care less" is an institutional phrase that compels us to remember our power must be tempered with mercy, which is expressed in the form of restrained indifference. Just as there is no real limit to justice/revenge beyond the constructs of liberal rhetoric, apathy is an abyss that must be skirted prudently. Without care, one could, without realizing it, become so indifferent to a subject that he or she neglects to even opine about it. On a large scale, this would threaten the core dynamic of what it is to be American: the unstoppable force of limitless guidance checked only by the immovable object of absolute unreceptivity to the guidance of others. "I could care less" is an enshrinement of self-discipline.
"I could care less but will not, for to care any less would render this subject unworthy of my spoken opinion."