You do realize that you answered your own question right?
"Why are bad words considered bad?"
"Because we, as people, decided they were bad"
You essentially rendered your entire thread pointless, but I'll bite and discuss the deeper issue that seems to be bothering you.
I want you to think about this statement: all meaning must be agreed upon, since unanimous agreement upon meaning makes communication possible. I cannot stress that enough.
It just wouldn't do to have one group of people call "bread" "knife" and another group call "knife" "bread". If these groups interacted, "pass me the bread" would be understood as "pass me the knife", and this would be an interesting interaction to see. So you see, when trying to come up with language, one must have an object that must be named, and one must be agreed upon with the rest on what the name of said object ought to be.
But here's the thing: if we want to insult someone, we have to choose a word and then give it meaning. I hope you are now starting to realize the obvious answer to your question. The reason we select a word like the F-word and designate a negative meaning for that word is the same reason we select any other word and give it meaning. An insult, an object, an animal, a person all need linguistic designations so that people can adequately communicate with each other.
So, stop complaining about why the F-word is considered bad. You already answered your own question. If you want to insult me, or if I want to insult you, I have one word out of many to choose from that I know you will understand because we are agreed upon it, and that's how communication has to be if it is to work.
It is what it is whether you like it or not.
