I read about that in another paper and it seems it is really, really common for people who are biologically related but who didn't know each other in childhood to be attracted when they meet...it happens in about 50% of cases. I had no idea it was that common.
I'm pretty liberal about sex stuff. I figure two or more consenting adults can do what they like, it's none of my business. I wouldn't personally want to fuck a family member, but if other people want to, it's up to them. As for preventing people from having children due to the risk of genetic defects, as long as we don't prevent other people from having children when there's a demonstrated risk of genetic defects, I don't think we have the right to prevent these people from having kids. Mind you, I don't think having children should be a right, but since society treats it as such I don't think we have compelling grounds to prevent it in certain cases and not others.
In this case, you'd think her own experiences of being abandoned by her father would have taught her that this guy isn't a reliable and involved father. If he dumped his family when she was a kid, he can do it again when she has a kid. I will never understand why women want to breed with such losers. From his side, it seems like a winning strategy...in 16 years he can date his (grand)daughter.
