It’s weird how pervasive this idea of entitlement is in popular culture, although I don’t think Nice Guys™ are necessarily a single phenomenon or just due to misogyny. It seems to me that there’s a mixture of gendered expectations of relationships (what you should provide, what you can expect, what certain expressions mean in different contexts, etc.). There’s an interesting discussion of the prototypical Nice Guy here: basically someone who uses a pretence of being nice or interested in another person in order to get into their pants. They aren’t actually interested in the other person as a person at all, and become manipulative or abusive if rejected. Even if the woman goes out with them in the end, the Nice Guy uses the information shared with them in confidence to emotionally manipulate the woman. Alternatively, the Nice Guy is never clear about their intentions and comes to resent the woman for her rejection of him (and other guys for being with his unrequited love interest), despite the fact that the issue was never raised. The Nice Guy ends up feeling that his ‘investment’ hasn’t paid off and the woman has cheated him, but the woman feels a huge sense of loss on top of any manipulation or abuse he gives her, because someone she saw as a close friend never saw the friendship as anything more than a means to an end. That friendship that she valued so much never even existed. There are plenty of examples in the post and comments to back up the claim that these people exist in significant numbers.
On the other hand, there are a number of possible scenarios that could lead to a similar kind of relationship forming, and I think there is a female version of the same stereotype that does less damage to men, but can be similar to a more innocent version of the Nice Guy. Sometimes guys are just introverted or have an idea that sex or a desire for sex is impure, so while they can’t bring themselves to ask a girl out, they will try to express their love through listening, kind actions etc. They’ve heard that women want someone who understands them, is willing to listen, isn’t just after sex, is willing to be a good friend and value them as whole persons etc., so they try to be that person. They do value the friendship, but they also want to go further in the relationship and hate to see their efforts being ignored (as they see it; it may well be that she has no idea), while other people who ‘break the rules’ have more success. Not only that, but by supporting the manipulator model despite repeatedly confessing how little the guys respect her, the guy starts to doubt that the woman really wants a sensitive guy as a boyfriend at all. In their minds, there are only two options: be the sensitive friend, satisfying his desire to be a nice guy and respect women (but remain that way forever), or be the manipulator who sees the whole thing as a game (but satisfy his desire for sex or a romantic relationship). Unfortunately they have a very formulaic and reductionist veiwpoint that ignores a healthy model of sexuality and relationships. I don’t think they’re trying to be manipulative here, but they will just end up with resentment if they carry on this way.
I think there are also women who are quite aware of the Nice Guy’s interest, but they will lead the guy on for the sake of their free moral support. Rather than just being friendship, the woman shows very little interest in the guy but will use his obvious attraction to her to get him to fulfil her emotional needs. The guy won’t leave because she will never be clear that a romantic relationship is off the table, but in the end the guy feels that he’s been used and that the relationship was never genuine in the first place.
I think the second scenario is similar in some ways to women who feel that sex is basically only for marriage or a long-term, committed relationship. However, they are willing to have sex with their boyfriend because they think it will make him want to marry her. Marriage was never really on the cards and it doesn’t change his mind in that area, so he’s happy to accept this change in the relationship without proposing. She feels that by accepting sex, he is tacitly agreeing to bring the relationship to the next level, then feels used when nothing happens. The guy could also have no idea in this case, but could also be using her hope of a longer term relationship to get what he wants out of the relationship without being clear that he doesn’t want to commit to marriage, family etc. A friend of my wife has been in and out of this kind of relationship for 15-20 years, but her resentment leads to low self esteem and suicidal depression rather than hatred towards men in general.
“Men give emotional intimacy expecting physical intimacy, women give physical intimacy expecting emotional intimacy” is a stereotype, but in my experience people’s expectations in this area are often strongly influenced by cultural ideas of gender. The resentment comes from an idea that these are the rules that relationships should follow, and failure to follow these rules is a sign of dishonesty in the other person. I think the idea of what makes a good relationship has changed a lot in the past decades and many people are not on the same page about the signals they give. There are also a number of unrealistic expectations that people buy into (the woman should be passive, have certain physical characteristics, respond appropriately to the man etc. vs. the man should carry the relationship, complete the woman and be sufficiently rich to negate the need for her own ambition). Being clear about what you want from a relationship and aware of your cultural biases while knowing when to walk away for the good of both people is a good start to avoiding these unhealthy relationships (probably not as much in cases where one partner is basically sociopathic, but more so where it’s a case of misunderstanding and unexamined privilege).
N.b. I’m not claiming equivalence here; these scenarios mainly cause damage to the woman and are clearly influenced by a patriarchal culture. Still, I think it’s useful to think about why someone who genuinely wants to be a nice person would get it so wrong.