Two consenting adults, including relatives?

[Optimistic Mysanthrope]

To each their own, so long as any relevant inheritable defects can be prevented by genetic manipulation, or reproduction is simply not permitted.

Inbreeding isn't as bad as is popularly depicted. It really only increases the emergence of recessive traits found within a particular family that may be harmful. With a little genetic screening it can be mitigated in groups of inbred populations.

Humans and other animals, though, have a natural aversion to mating with close relatives they were raised around.

Plus there's the ick factor.

Kinda sounds like people think that incest is ok, but only if controlled by eugenics. The "moral decay" guys are gonna love this.