BAD WORDS!

How did bad words become bad words ? I've always been curious on how they ended up being bad. Were bad words purposely written bad or did someone start saying they were bad. This topic frustrates and confuses me. This hurts my brain just thinking about it and not knowing the actual answer to this. For example, the word "bitch" originally means a female dog. But I'm so curious about, how did someone turn this word into a bad word. So does that mean I can change a good word to a bad word ? For me, bad words are okay but it depends. If you're going to use it to hurt or offend someone, that's when it crosses the line. But using bad words as in if you stubbed your toe and blurted out "F*ck!!" then that's okay. If you hear someone full out cussing with their friends just to be cool, of course you're going to think bad about them. So yes, bad words does change the understanding between people but it all just depends on how you use them and say them.