I think this is a variation of the "savior dream" that people of all ages and preferences have. It may be more prevalent with us to a degree, however, because our situation in society causes us to have a strong yearning to find a kindred soul who will understand us, and who we can be there for and understand in turn like no one else could.

It's also part of the deep yearning to be needed by the person we love, even though it's much better to be wanted without being needed, since gratitude isn't the best foundation to start a relationship on. But the basic emotions behind this yearning are indeed noble, because we want to care for girls (or boys, in the case of BLer's like my bud Godspell) who most need to be loved and cared for. We know many of them have tumultuous lives, and we want to save the people that we love, and to make a real difference in their lives.