I'd say physical. It takes up our Doctors in a devious way, because they knew the consequences. Psyche? I don't follow how it would, taboo aside.
eta: again, it's also an abuse to the child they have.
we are talking about anyone marrying anyone without regards to gender.
you stated that is fine, but you had the one exception of blood relation (bother/sister) becasue you said it would "harm society"
Im interested in your definition of "harm"
you gave an example of the physical (genetic defectivness)
Im asking if the psyche of the nation/the people is included in your definition of "harm" (this leaves off the example of brother and sister and returns to the overall marriage "free for all" youve espoused)
I do not include psyche, because the psyche of the nation was once racist, was once sexist, was once a lot of things that were wrong. Psyche to me isn't a prerequisit for doing right by people in the minority. Physical harm on society, on the other hand, is different to me than psychological.
And being honest, I didn't delve this far psychologically about why I wouldn't mind Gay marriage, because they can only "harm" your psyche, AND if you let them. My convictions and my teachings to my kids will have the utmost confidence in-self, not worried.