How Can A Word Be Bad?

Why is fuck considered to be a bad word? Did it pee on the carpet or something?

"Bad dog, peeing on the carpet is bad."

"Bad fuck, peeing on the carpet is bad."

Isn't fuck a good word?

"Fuck, fuck, fuck!!! Bad dog!!! Peeing on the carpet is bad. Who the fuck is going to clean this up?

See, it's a good word.