Men want to get laid. Period. This is the only stereotype that I can point to that is almost never shown to have an exception. The point of this post is to reinforce the idea that men can't 'just be friends' with women and that women should embrace this aspect of their relationships with men. Sex is always part of the equation. This phenomenon is biological, psychological, and cultural in its rewards for males proactive in seeking sex.
Subsequently, women are ordained the gatekeepers for sex. There is a real biological reason for this phenomenon: women have 'the goods' in terms of reproduction. A man can fertilize thousands of eggs with almost no cost to him in the strictest biological sense. Each sperm contains less protein, energy, and nucleic acid than what one might sacrifice by scratching the end of their nose. A woman, on the other hand, spends ten months unable to escape a growing fetus that might kill her just through it's delivery from her body. It parasitizes her bloodstream and if she's malnourished, the fetus will thrive at her expense. It's estimated that this experiences ages a woman 3-8 years all the while risking gestational diabetes, autoimmunity like lupus or celiac disease, kidney failure, potentially fatal blood clotting and hypertension, and pregnancy induced tumors. If it survives to term without killing her, it will continue to parasitize her if she chooses to breast-feed it. Breast milk is literally organized breakdown of mammary tissue.
Obviously this is where the whole gate keeping aspect arrives: if the woman makes a good choice in terms of mate, he'll stick around and at least try to compensate the enormous biological burden she's carried or care for the offspring outright if she does not survive the process.
This gets into the psychological and cultural aspects of sexuality. Men hit on a lot more women than women hit on men. It's a numbers game for a guy who doesn't have much going for him or even one who does; if he hits on enough girls, eventually one will sleep with him. Of course this is why women don't take rejection very well; we're used to men making the effort because they don't have much to lose. I digress. Men want to get laid.
Ladies, if a guy says he wants to be your friend, he really means that he wants to sleep with you. There are a few cases that you might think are exceptions to this rule.
1. You're unattractive - this could be as simple as him being gay or that huge mole on your face but I bet if you were cell mates in prison, he'd still do ya;
2. He doesn't want to jeopardize a relationship - this doesn't mean he wouldn't, just he's got a decent reason not to sleep with you. He might even be keeping you around for the attention or as a spare. Note also that the relationship he's protecting doesn't have to be romantic, it could also be a work relationship or one of his homeboys;
3. He wants to sleep with your hotter friend - still, this isn't to say he wouldn't sleep with you but he's smart enough to know that girls usually don't pass guys around and if he sleeps with Betty he's blown his chance to do Veronica... though it never really stopped Archie - damned soulless gingers;
4. He's your father, brother, or other close relative - Even if not for social taboos, we're actually hard wired to feel disgust at incest. Still, if you were stranded on a desert island... ewww;
5. You don't want to sleep with him - implicit in this scenario is that the girl is maintaining the 'friendship' status unilaterally, he might agree with you superficially but he probably imagines you naked while romancing a tube sock;
6. The rare exception is a guy who actually wants to be your friend but not get into your pants. I have never met one of these.
So girls, next time a guy says "I just want to be friends" or your significant other says, "she's just a friend", take pause. You may have been given useful information. This is subtext in negotiating sex and relationships.
Sadly, a lot of women don't realize the power of sex in relationships. With tragic frequency, accomplished ladies lower their standards or even pair off because of social pressure or cultural norms often not anticipating the consequences of poor mate choice. To add insult to injury, men have coined terms designed to further lower our expectations: a girl who wants a man with a reasonable income or just a job is a 'gold-digger'; a woman who demands fidelity is 'jealous'; a lady who seeks an educated man is 'stuck-up' or 'conceited'. The list goes on and while there exist women who have an overwhelming sense of entitlement, the majority of women who are labeled one of the former are simply exercising their biological imperative to discriminate.