Hard topic forme. It seems flat out wrong from a moral and a genetic standpoint, but if two people love each other, I don't think we have a right to oppose it. I would have to say it is okay as long as it isn't an older brother taking advantage of his younger sister or vice versa. This is kind og like homosexuality for me, somehting that I would never do but is okay. For some reason I find it harder to come to terms with this one though.