Shit, Ass, Damn, Piss, Fuck

[Cinjin]

The strange emotional power of swearing - as well as the presence of linguistic taboos in all cultures - suggests that taboo words tap into deep and ancient parts of the brain. In general, words have not just a denotation but a connotation: an emotional coloring distinct from what the word literally refers to, as in principled versus stubborn and slender versus scrawny. The difference between a taboo word and its genteel synonyms, such as shit and feces, cunt and vagina, or fucking and making love, is an extreme example of the distinction. Curses provoke a different response than their synonyms in part because connotations and denotations are stored in different parts of the brain.

This seems the best explanation I've heard on the subject to date.
It's not the word itself, it's the connotation that it carries. Slender versus scrawny really drove it home for me. However, were I to play devil's advocate: I always felt that the word shit was just a word to describe feces and that the word poop was just another slang term; equal to and no more offensive than the word shit. I've even heard the expression, "So what's the poop on that?" when requesting information.
It would seem that words that are found to be profane are only found to be profane by the crowd you keep. My mother hated the word "poop" and wouldn't allow me to use it as a child.

Perhaps, profanity, like morality is not objective and those who get upset about it are projecting their own subjectivity.

??