People who use "retarded", "gay", "autistic", "ghetto" (and so on) in a derogatory form are showing a lack of imagination, aren't introspective enough to consider how their choice of words makes others perceive them, and trivialize an entire group of people by subordinating them in their effort to demean someone else.
And that's the problem. It's condescending (and meant to be, don't tell me it's not) to call someone or something "retarded" when one is actually expressing an opinion that the person or thing is not worthy of merit, and history is rife with abuses that result from trivializing a group of people by distilling that group to a pejorative. "Fuck those short sighted motherfuckers," may shock because of the direct use of the glorious and multitalented root word "fuck", but it certainly isn't trivializing a group of people with a minor vision impairment, because short sighted is not the term used to refer to someone who is near sighted. It's borderline lazy, sure. It may offend someone's sensibilities, yeah. But choosing a word that one knows damn well trivializes a group of disadvantaged human beings ... that's profoundly different from dropping the occasional F-bomb.
It's not about political correctness, it's about recognizing that one's choice of words can carry a great deal of meaning that diminishes the intended effect of those words. In some cases, by literally dehumanizing a group of people.
It's not "colorful language", it's lazy and careless prose.
And to any current reader of this comment who thinks such pejorative language is okay in civilized company: either this post changes your mind, dear reader, or it doesn't. Using what you think to be clever analogies, closed-minded logical fallacies, or meritless affirmative defenses ("but, freedom of speech!") is encouraged, if it makes you feel better about yourself to put me in my place for feeling the way I do about this kind of language. Your right to free speech is no different from mine, I won't stop you. But I also won't waste the expression of my free speech rights by trying to argue with someone who doesn't acknowledge that maybe ... maybe ... they're wrong, so please feel free to satisfy that desire to get in the last word.