Because of the societal agreement that has been placed on them as such. The word "spinach" could be used as a cuss word if everybody had that interpretation of the word. The seven "bad words" that George Carlin made a comedy sketch about just have that societal interpretation as "bad" and not suitable for the public airways. It ain't a bad or good thing. It's just a thing. Listening (the interpretive part of hearing, seeing and physical feeling) gives meaning to our experience. We are always trying to "make sense" of our physical world experience through the private conversations we have with ourselves non-stop. We live in a sea or ocean of private conversations and assessments about what is going on. Things are interpreted as "makes sense/doesn't make sense" "right/wrong" "good/bad" "like it/don't like it" all the time. There are no absolutes, just interpretations. You're doing it right now as you read this - having an interpretation or "listening" to the words that are being filtered through sight. Just remember a "chair" in the Western world is not a "chair" in some primitive tribes that exist today. Dig on that awhile. I wouldn't get too hung up on cuss words. It's just a societal thing you have to put up with.
What is the difference in fighting yourself, and fighting others? I mean...In order to find yourself you have to fight the perceptions you've created for yourself with the situations that you've but do you necessarily have to fight others to do it?
Then again....what does fighting mean?
Isn't fighting just the opposite end of resolving?