Well, if you think about it, anything that's open is vulnerable and subject to damage/offense/wounding. A posture, a home, etc. So, "openness" isn't really a better term. If you share the things you feel sad/scared about, you can be hurt by someone who does something insensitive with that information. If you share the things that make you light up with joy, you can also be hurt by someone who does something insensitive with that information. Patriarchy has conditioned some men to scoff at the word "vulnerable," but the term is neither here nor there: it's all the same concept, with the same potential result — pain. But it's one of those "no risk, no reward" / "fortune favors the bold" sorts of things.

Or to borrow a man's words... my grandfather raised his kids with the following saying: "A real man cries, because a real man doesn't give a shit what other people think about him crying." In other words, vulnerability is true strength; true strength is the ability to embrace ALL of your tender emotions without feeling diminished or cowardly about them, knowing that you'll be able to weather anything that comes with them.

In this sense, the most vulnerable people are the bravest, the strongest, and the most resilient. That's why women (healthy ones, at least) find it such a sexy quality.

At least that's how I see it. :)