Who decided that certain words were bad to say?

Answer 1

"Bad words" are usually defined as "bad" based on them referring to taboo topics or respected things in a disrespectful way. In English many of the "bad" words were simply the words used by common people to refer to things that the elite had a "better" word for - because the nobility at the time spoke French and the commoners only spoke English, which the rulers found gauche, uncultured, and - vulgar. Remember that a definition of the word "vulgar" is "common, ordinary," from Latin vulgaris, volgaris "of or pertaining to the common people, common, vulgar, low, mean," from vulgus "the common people.

Who decides what words are bad?

Those who have enough influence to declare what is taboo and those who have enough influence to declare what subjects should be revered and respected and thus not denigrated in language. What is a "bad" word to one group may not be considered of any note to another because of differences in values and morality.

To a person who reveres Jesus - using his name as an expletive is offensive and makes it a bad word in that context. To a parent who considers excretory functions and excretions to be impolite to speak of directly, any direct reference to them by a child constitutes a "bad" word.