Ok, that's creepy, but if they are 30 and 50 what's the problem? My point is just because I don't like something does not mean I get to stop people who are not hurting me from doing it.

There was some story about people who where both adopted got married and then found out they where siblings. And yea it's creepy, but while I would be ok forbidding them from having children (for the public good) I don't see the value in forcing them to break up. And, even forbidding something on genetic grounds becomes a slippery slope problem because it's one step from their to sterilizing people.