Women with a high libido (generally defined as having or desiring more than 7 orgasms and/or sexual encounters in a week) often struggle with social acceptance of their sexuality. They are typically labeled as sluts or whores, and taught that their sexuality is a negative, dirty and unladylike thing.
Many of these women also report having being labeled as being sex addicts, today's version of the nymphomaniac label. One woman in an article by Eric Blumberg reported being labeled as a sex addict by a therapist after she disclosed that she goes out on weekends "to get laid." The woman's response was that "I like it, but I'm not addicted to it, I'd probably be miserable, but I could go without it." When the woman further admitted that she masturbated daily, her fate was sealed, in her therapist's eyes: "The way he was talking, it was awful for me to be doing this." (Blumberg, Eric. 2003. Lives and Voices of Highly Sexual Women. Journal of Sex Research, 40,, 2, P 150). Such women also usually report having have more male friends than female, as they say that men understand them better, and don't stigmatize them for their sexuality.
I've heard this from many highly sexual women, that they typically have few female friends. When they do, these friends tend to also be women with high libidos. But for the most part, these women prefer to associate with men, where they can just be themselves, and not worry about conforming to the expectations of other women.
Why are women threatened by other women's sexuality? Perhaps it's frightening - women are taught to suppress their sexuality, and when they see another woman reject that teaching, it might trigger an internal conflict in other women, where they start wondering and fearing what it might be like if they also started to express their sexual desires. When men have a conflict with another man, it is usually out in the open. Evolutionarily, open, public aggression and conflict in males was rewarded, as females mated with the winning male. Female aggression is rarely public, and not rewarded when it is. I can't say that I've ever seen the hottest guy in a bar walk up and sweep a woman off her feet after she wins a catfight. Men might fantasize about watching two women fight, but the reality of female conflict is far less sexy, and frankly, far more damaging to self-esteem and female rights, than male conflict is damaging to men.
Others suggest that this female-to-female conflict is a holdover from the days where a woman's sexuality and her reproductive capacity were the only economic resources that a woman had to trade, in exchange for support and care for her and her children. And why should a man buy a cow, when he can get the milk for free?
Shows like Sex and The City and Hung are now beginning to celebrate female sexuality, between women. Hopefully this trend continues. Till then, the ugly world of covert female sabotage and aggression towards other women will continue.