In prehistoric times, men naturally could have sex with as many women as they wanted because it carried no commitment. Women, on the other hand, had to make a massive commitment because having sex with one man put her in a position of vulnerability for the next 9 months, and longer while she raised a child. This put men in a position of power, because women needed men, while men weren't dependent on any one woman. This remained true until women began supporting themselves, which has become more and more possible over the centuries. Why don't men respect women now then, you ask? The answer is a very simple principle. People respect you as much as you make them. Every woman who has respect made people respect her. The problem is, there are far too many women who are content to let men keep the upper hand and don't bother to stand up for themselves, and pursue men who don't respect them. I'm sure you know the type. These girls exist because that mindset is still partially hardwired into female brains, and has only been evolved out over thousands of years. The problem is, the men who didn't respect women then were the ones who didn't need to, because they were good enough hunters that they could support many women, and the women came to them. The men who did respect women did so because individual women were valuable to them, primarily because they didn't have the evolutionary viability to attract multiple mates. It all really comes down to natural selection. This is still somewhat true, in that men who can sleep around a lot respect girls less, because no girls make them do otherwise in order to have sex. Men who can't sleep around as easily respect women because they value the ones they have. Not to say this is always the case. There are the hopeless angry people who hate girls because they never get any, and the people who can and have easily had sex with countless women, but stopped out of respect. I'm just pointing out a noticeable trend that supports my theory.
The girls that continue this system teach men that they don't have to respect women as a gender, so women have to fight an uphill battle for respect and power. Women need to realize they have a monopoly on sex, and they can use that power over men if they do it together. If just one girl says no, the guy can just go until he finds one that says yes.