A fundamental claim of Red Pill Theory is that men are treated more harshly by society for sexual misbehavior. For instance, an older woman hitting on a younger guy is often tacitly accepted but if an older man hits on a younger girl he is easily labeled a creep. In many states, it's assumed that if both parties are drunk and have sex, it is the man who committed rape. In ancient mythology, beautiful women are often presented as deceitful and manipulative (with these qualities often contributing to their attractiveness), while a lying man is always disgraced. In my personal experience, girls are willing to string guys along, manipulate, and tell lies to be "nice" in ways that seem absolutely abhorrent to any masculine moral ethic. For a long time, I've thought of this as selfish, and thought that society's acceptance of this type of behavior is a mark of corruption. Now, I'm not so sure.

I think the greater sympathy we have for women in sexual relationships comes from the different meanings of sex for the different sexes and the benefit that societies reap from women's ruthless sexual choice.

Imagine you're in an ancient city (like Troy) and all of the women get full choice over the paternity of their child (men have no say). They can either sleep with people at random or they can sleep with only the biggest, best, and smartest men. If the women choose the best men then your city will not be sacked, and most likely you will be able to go out and conquer new lands, at the very least you won't starve. In having a kid with whoever the prime male is at the time, women are benefitting the community by having the most competent offspring. Because the civilization wants the best possible kids and the woman wants her children to be reproductively successful, her personal goals and the goals of society align.

A man's interests in reproduction does not always align with the best interests of society. If a weak guy wants to get his genes into the next generation, then society suffers because they invested resources into the production of a child who could have had a greater yield if his father was better. Therefore, women's sexual interests necessarily align with society's but a man's sexual interests don't necessarily align with society's.

If we take this lens and look back on feminine sexual "immorality," we can understand the more ruthless women are in getting babies produced, the more a society will flourish. If a girl is "selfishly" stringing a guy along for resources, or lying to be nice to a guy who doesn't have a chance in hell, or even cheating on a spouse, the society that encourages her in that behavior, or gives her valid ways to justify it ("she didn't' feel loved") will end up with better kids. So long as women get the job done, then we all benefit, so long as we aren't the guys used by the girl in the process of child development.

TL;DR: We accept women lying to and manipulating men more easily because it benefits society at large. Anything a girl does to get the best genetic material and to get resources allocated to her kids is in the interest of society because the society produces better kids.