In the second edition of her book, CUNT, Inga Muscio admits “I am most often aware that I am a woman when I feel threatened...” In the same vein, Simone de Beauvoir quipped that one is not born but, rather, becomes a woman. What unites roughly half the population is not genitals, chromosomes nor hormones and what turns a child into a woman is not menstruation, penetration nor childbirth. No, it's the shared experience of playing second banana, as it were.
Whether you're overlooked because you're a woman or you're picked because you're a pretty woman, the problem remains the same. And this problem has been rampant the world over for millennia; it unites generations of women more strongly than any reproductive function. In this harsh world of competitive and weak human beings, man* needs to make somebody #2 in order to keep himself #1. Who better than not-man? And there are many women who push someone else, a masculine woman or a feminine man or someone else entirely (or even a prettier, more feminine woman!), into #3. This is what puts the “sexism” into “heterosexism”: insecure people pushing down queer people just to ensure that they're the ones rising up. It's bullying, all the -isms are just bullying on a larger scale!
There are women who claim to never have experienced sexism. They're either extremely privileged and cloistered or blind to, well, everything. It begins when parents proclaim upon birth “that's not a penis, bring out the dolls and pink frilly dresses!” for one and “that's a penis, give him a toolbox and blue overalls!” It is a privilege, usually tied to class, to have been brought up and then to continue in adulthood otherwise: not as a #1, a #2 or as any rank at all.
* I don't mean all or even most men, nor even just men in general. Clearly, Phyllis Schlafly has done more to perpetuate heterosexism than RuPaul.