Hmm,
Personally, nobody in my immediate family does it for me.
I was going to make a snarky comment about breeders, but then I remembered that my favorite porno was those Spanish twin brothers.
I was going to comment on vice is nice but incest is best then remembered that my red-neck family has at least one half-sibling breeding pair.
I was going to describe my moral outrage then remembered that one of my favorite authors is Heinlein.
My disgust at this impropriety knows no bounds and I'm going to go right out and burn my Scottish genealogy...cause on those windy, rainy islands right up until 1912 first cousin marriage was the norm in my family, not the exception. How horrid that my favorite grandfather was the child of such a marriage, worse - one set of his parent's parents had married each other after the death of their respective brother and sister! The horrors of it all! No wonder he used to say our family was part selkie...what were all my ancestors thinking in the outer Hebrides!
Ultimately, I was going to write a sharp letter to the editor when it occurred to me that my darlin' and I are, if not that closely related, also cousins.
So, I guess I'll just content myself with minding me own business and wishing them much happiness. The squick factor is our problem, not theirs.