A woman wanting her man to be emotionally vulnerable is selfish.

Women who want men to open up emotionally is hiding their own hunger for reassurance in knowing that their partner will respond emotionally to her. The whole idea is dressed up in a pretty package with the promise that it is for the man's benefit; it is not. Women feel security with a man who she knows which buttons she can press to create which emotions, and being vulnerable with her is giving her the instructions manual. This isn't strictly a bad thing, but it is strictly a selfish thing, because it gives the power in the relationship to the woman, but it's never honestly disclosed as a power grab, but rather as a positive for the man in the relationship that the woman is allowing him to emotionally express himself. The problem is of course:

1. Once you give someone the cheat code for a game, it's no longer interesting, exciting, or fun.
2. Reassurance only has value from someone who isn't constantly giving reassurance.
3. Not every button she presses leads to an emotion that she is okay with.

All of these things get conveniently left out of every conversation by women when they talk about wanting their man to be emotionally open, especially if they frame it as being for "his sake". Firstly, people may not admit it, but a lot of what keeps relationships together, especially early ones, are all the animalistic and exhilarating parts of exploring another person's body and mind. Giving someone the complete map to your entire inner world is tantamount to helping someone activate God Mode for your video game; it's not fun any more. You can certainly transition from passion into love and mutual respect, but why would you purposely take the fire out of your own love life?

Second, if you are constantly making sure that your partner has nothing to fear about you feeling negatively about them because she always know how to make you feel the emotions she wants you to feel, you are inflating your own reassurance currency. Women solve relationship problems by fixing your emotional response, instead of by fixing her own behavior that caused that emotion, and you are putting yourself on the path towards hyperinflation of reassurance and allowing the woman's behaviors to run unchecked by your emotional response to it, rendering your emotions valueless in the relationship economy.

And third, you don't know what she is prepared to emotionally handle and what she is not. Every woman that you tell, "Everything the light touches will be yours." is gonna end up asking "What about that shadowy place?" And if you don't want your partner to end up fighting Scar and the hyenas in the Elephant Graveyard of your psyche, you're gonna have to ration yourself with what you let her know about you emotionally and what you don't.

So what do men actually need from women to be reassured in their relationships?

Desire.

That's it -- And yet you don't see dating advice telling women they need to constantly demonstrate and make clear that they have desire for their man as frequently as they can throughout the relationship. Men don't have that same hunger for the absolute and all-consuming emotional coalescence of two human beings. Their reassurance in the relationship comes from knowing the woman desires him, because every man knows that if the woman desires you, you can feel secure in the relationship -- no woman ever ends a relationship without first losing her desire for him. Women are far more emotional creatures than men, and ten good logical reasons for breaking up with a man will lose to her one emotion of desire for him if it ever came down to it. Therefore, if the woman convinces the man that she is captivated by his style, drawn to his intellect, tickled by his humor, safe in his arms, electrified by his touch, satisifed by him in bed, the man knows on a visceral level that this woman will not leave me. And this is also very much a power play for men to get women to demonstrate their desire for him, for example by making her break her own rules just for him ("I don't have sex on the first date, but...") or pushing her further than previous partners ("I usually never do this, but..."). Because the man knows the woman loses leverage when she shows desire for him, the same way a woman knows the man loses leverage when he shows emotions for her.

The addendum to all this is, of course, there can be overlap in unique relationships. Some men engage in relationships with a more feminine role while some women engage in relationships with a more masculine role; but these are deviations and not the actual foundation of male-female relationships. The yin-yang symbol has a small white dot in the black comma and a small black dot in the white comma; don't let people try to convince you that the dot is bigger than the comma.