@slightlyflightyone These... are good questions. My first instinct when talking about incest is to go "oh yuck, that's wrong" - but if it's between consenting adults idk.

To claim that it's about preventing the birth of babies with certain disabilities and such (for #1) would fall into eugenics. One may worry about abusive power dynamics between familial relations (#2), but I'm not sure that's inherently the case. Interesting to think about