I find this quite interesting (I know some have been bored silly already ) because I feel, but have no empirical proof, more inclined to clueless's explanations than those you have propounded.

Also, the different uses of 'swear words' have been shown, to a certain degree, by our different use of the language in our explanations. You have used the word 'expletive' whereas I used 'invective'. They do, of course, have completely different meanings because of the circumstances in which the 'swear words' are used (there are other definitions, such as vituperation).

I was brought up in very working class areas - Hackney in North London and in the East End of London - and worked as barrow boy in the East End. Like many people I moved through a number of different jobs and changed my accent and and use of language to that which best suited the situation. I made a mistake, in one job, by not changing to the right accent and language but managed to recover from it quite well. I think that it's in the nature of people to want to blend in, so they use language and accent as camoflage. I have known some clever and erudite people who have used their natural intelligence to overcome their poor education but have been reluctant to show either their intelligence or, conversely, their upbringing depending on the situation.

The use of swear words, or the lack of them, quite often point up this fact.