Language changes. The meanings of words change. For example, resentment was once used to describe something someone thought of fondly. "Bitch" and "cunt" are no different.
While "Bitch" was once a derogatory term for women, the general meaning of the word has changed over time. In fact, its original meaning was innocuous, describing a female dog. In certain contexts, the term can still be used against women, but often the term is applied to men, too. In US English, "bitch" is the equivalent of a shady person undeserving of respect, no matter what their gender. It can also be someone who complains about things that are trivial, ("don't be such a bitch about it").
"Cunt" is another one. In US English it has been a particularly cutting and insulting word with a great taboo placed upon it. This made the term more powerful when used, (frequency of use does affect how we view words). In European English-speaking countries this word has not had the same effect. They use "cunt" as often as we use "asshole" over here. In fact, in French, the term that translates to "asshole" is "con" or "connard," which, a hundred years ago, was the word for a woman's vagina.
Internet forums demanding those two terms be treated like racial and homophobic slurs are actually giving those terms more power than they have or deserve.
The "N" word was once used to describe an entire people who were oppressed, murdered and sold into slavery.
Bitch was used to insult a woman who wasn't following the rules of lady hood and respectability. There are some major differences there.
The "F" and "N" words are still used in much the same way they used to be. "Bitch" has undergone a lot of changes and has a lot of different meanings. Perhaps we should instead focus on the way we talk to each other and disagree about things rather than the words themselves.