Claiming that vulnerability is a moral virtue makes the mistake of putting vulnerability on the wrong side of the ledger. An existential term, it is made to pose as an ethical concept. Jonathan Lear helps us see why this is the case.
For in Radical Hope Lear advances the metaphysical thesis that human beings are finite erotic creatures. We are creatures of finitude in the sense that we are limited in a whole range of cognitive, affective, and volitional capacities: there are unsurpassable limits to our knowledge, to our emotional states, and to our wills. We can only know so much, feel so much, and do so much and no more, and there is no getting ultimately beyond this (call it) existential state of being human.
Quite naturally, our existential condition as finite creatures entails vulnerability and dependence on others. My vulnerability flows directly from my finitude. I am susceptible to injury, harm, and illness just because I am a human being and not some other creature. (Of course, I can become less susceptible to such things, and this is one sense in which one can speak of learning or of adulthood.) Dependence is also bound up in finitude. If I can only know so much, then I may need to ascertain from others what is the case (e.g., what time is it?). If I can only do so much, then I may need to ask for assistance from others (e.g., can you help me move this couch?).
Our existential state of finitude urges us, Lear thinks, to reach out in longing; this is the erotic energy of the human being. I reach out to my lover, despite the attendant risks, in loving. I reach out to knowledge by means of inquiring into what I do not know even though I may come up empty. I reach out when I act, expanding thereby the bounds of my grasp, in spite of the distinct possibility of bringing about unintended consequences.
If this is the correct interpretation of the thesis that human beings just are finite erotic creatures, then it immediately follows that vulnerability is on the existential side, not on the erotic side, and it is only in eros that we can exercise moral virtues. Thus, vulnerability is on the wrong side of the ledger when it is deemed a moral virtue.
The phenomenon in question–the one misdescribed as vulnerability–is actually courage and truth-telling. What those in business circles and in creative leadership mean to say is that when John acts courageously by (e.g.) telling the truth, he is facing up to his finitude and going beyond whatever fears he has because he believes–and this with good reason–that the good matters more than the unpleasant. In other words, John is learning that courage and truth-telling trump whatever displeasure may be associated with doing or saying what could evoke fear (of death). For there is, he must grant, something beyond, higher, more important than his death. This is what he learns to honor and uphold, and thus insofar as he is courageous and truthful he is worthy of our praise.
(There is a longer argument to make about the loss of thick moral concepts, an argument that would demonstrate how the loss of such concepts made it possible for some unsuitable terms such as vulnerability and discomfort to enter the scene. Here see Alasdair MacIntyre, After Virtue.)