Scandinavia and the World

Comments #9849986:

Old habits die hard 1 12, 5:46pm

I think it depends on if they have issues that could be passed to their children and/or if incest proclivity is somehow genetic, IE that they are likely to be incestuous too.

There are already plenty of people with out incest whom by these measures shouldn't be having kids. Lots mental and physical diseases that someone's life a lot more challenging, if not needlessly so.