>>Remember that in the Judeo-Christian tradition suicide is a major sin. This is why Reki was born with black wings
No. Reki wasn't born with black wings; she was born alone in a dark, cold, boarded up part of Old Home, where she surely spent a number of hours until her wings sprouted, with nobody in sight to care for her. She then lay there on the ground, covered in blood, probably in great pain, still cold and very much alone in the dark, boarded up room, until a Haibane found her. Wouldn't you feel like nobody in the world cared about your or wanted to help you? That's why Reki has black wings, and that's whys she's sinbound. It isn't that she was BORN that way as a Haibane. if she had been born normally, she may very well have developed just as well as any other normal Haibane. But she had the unfortunate luck of hatching out of her coccoon in a cold, empty, dark room with nobody around to care for her. It subconsciously reinforced to her the idea (to which she was already susceptible) that she really is alone, and that, in fact, nobody really cares about her. That's why she has black wings. It's not because she committed suicide.
As for the other Haibane, I don't think anybody would argue that EVERY ONE of them is a suicide, but I think the case for some of the Haibane having committed suicide is pretty good, particularly Rakka.
