Answer:
i believe people started using them and then they decided they sounded wrong so they said if u say that word its not correct manners
You probably want to distinguish swear words, curse words, and vulgarity. People have always emphasized the truth of what they say by swearing on God's name or something sacred such as putting hand on Bible. To cry out God's name in vain, that is without a solemn purpose of attesting the truth, is offensive to religious people. Second, people have always expressed their contempt for others by wishing them harm, as to be damned (to hell). To express such an eternal form of ill will is also offensive to religious people. Vulgarity is talking in public about private matters such as sex and bathroom activity, and you know all those offensive words too. People do all of these things to make other people mad. All of these words have become so common that the sting is gone out of them, but they are still not polite forms of speech.