Connotation is your friend.
"Cocksucker" was originally conceived as an insult against male gays because it was comparing them to women by saying that by indulging in practices similar to straight females, you are not a man and there is something wrong with that.
So it's actually a term that marginalizes gay men AND women by proxy.
Also, implying the word cocksucker is ever used in the context of a woman. It's either a slur directed at a gay man, or it's a generic insult at males in general because it is associated with homosexuality, which is bad. That is the connotation of the word.