First off, let’s set the record straight regarding swearing, cursing (or “cussing”) and obscenities. They are three different things.
Swearing (or oaths) is actually very rare in our society – it refers to calling upon a higher power, usually God in a Judeo-Christian culture, to witness the truth of what one is saying, just as in any swearing-in ceremony. “”By God…” or "So help me God..." are the most common examples, although I thought Long John Silver’s “By the powers” was rather quaint.
Cursing is much more common – once again calling upon a higher power, but in this case to punish the person or object in question, “Damn it!” probably being the most common usage; damn of course meaning to consign the person or object in question to Hell.
Obscenities or vulgarities are primarily what we are discussing here – words used for various body parts or functions. Why these old Anglo-Saxon words are considered crude and vulgar while their Latin-based equivalents are not is not really clear, but I understand it goes back to the time of William the Conqueror. When French-speaking William conquered England, French became the language of Court and the old Anglo-Saxon tongue became vulgar and uncouth – the language of peasants. Why the words for various body parts or bodily functions (particularly copulation) survived as obscenities is not clear, but I suspect it has something to do with the bizarre concept held by many in the Christian-dominated culture, both then and now, that the human body is evil, and anything relating to its more intimate parts or functions is gross and disgusting. Hence, the most vulgar of words for the most vulgar of things held the most shock value.
Joseph