I've often wondered about this - nearly everyone in the world is guilty of it, yet in many cases it is treated as a crime or a serious offence.
Of course, there are the two extremes - for example, the truckers (no offence to any truckers or relatives of truckers) in general, swear a considerable amount, in comparison to the one-word wonders that usually proceed an injury or loss of something.
What also occurs to me, is that swearing can be, or will be used in nearly all situations, such as:
Surprise - Being made to jump or scream
Anger / Annoyance - Usually aimed at an individual or group, or in some circumstances, an item
Happiness - Used to express the entend of ones enjoyment / happiness
General Conversation - The people who swear every other word, to no effect
you can probably think of more, but these are the first that crossed by mind.
What makes you think though is the fact that although everyone does it, many think that it is now a part of life, when yet it effectively achieves nothing. It only has as much effect as the receiptient is prepared to give it.
At some point in life, the universe, and everything, some people must have 'created' these words that nowadays play such a large part in our lives as a whole, and quite often cause great offense.... but how? Did someone decide that they wanted a horrible name to call an enemy, and it grew from there? Why bother?
So, why do some people swear excessively? Does it really make them seem 'hard' in the eyes of others, do they really think that it will improve their social status by doing it? I grant that in these causes, 99% of the time there is a strong influence such as parent's that constantly swear, or friends... but then we get back to parents eventually, and they got it from their parents, etc, etc.... but back to where? Where did it originate, and for what purpose? And what's more, why are some words deemed more offensive than others. Furthermore, different people find different words offensive. Some familes as a whole swear far more than others, yet for no apparent reason.
Of course, there are some exceptions... such as words with meanings that have changed over the years, such as:
'Gay'
Not many years ago, that term basically meant happy. Yet, over the years, it has been adopted by the ever-increasing vocabulary of offensive / swearing words, it is now treated as either the term for a individual 'keen' on their own sex, or a word that effectively disregards gay people. You may be thinking "gay" isn't a swear-word, and I agree, yet now it is used in the same manner as many other swear-words, and yes, people do find it offensive.But, to return my point, "why do we swear," used in general context, what does it achieve? Emphasis?
You decide.