The practical problem is, of course, enforcing this prohibition on procreation. Forced sterilisation is difficult to sell and problematic because the subjects might wish to have children with other people. RISUG might be a solution, once it becomes available.

I'm not sure what I think of the fact that everyone is concerned with the genetics of possible offspring in the case of incest, but nobody minds two chronically depressed, highly neurotic people, one of whom has a hereditary autoimmune condition, procreating... (The domain of quantification for the slightly hyperbolic "everyone" and "nobody" here is the general public rather than LW. I suspect that many in this community would, in fact, mind the latter case as well.)

Because it's good ethical practice to try to work out what to do with controversial issues when the answer is not completely clear.

I see no visible controversy around the issue.

There's a reason why that German ethics council thinks it should be legal.

I don't read German except with more effort than this is worth, although I note that it begins by mentioning a case of a brother and sister having four children together and public consternation over their prison sentence. What reasons does that report give? It is that it considers the German law as it stands an unsatisfactory way to deal with the undesirability of incest, or that society should recognise incestuous relationships as equal to all others? There is a big difference. How does the report propose to handle the negative consequences of inbreeding? Or have you not read any further than ryot.org?