Well yeah but I mean what if the two kids want their own children together? I'm sure they know the outcome.
incest children dont come out "handicapped" or "missing fingers"
they will carry common family genetic disorders that are strong to them both specifically, 100% to the child.
if they both have the weak gene that goes through the family, say; both are alergic to cats. then the child will be born allergic to cats. and that gene isnt bred out of the family line yet.
it wont just create new issues. incest babies carry bad genes guaranteed. however every one of us here carry bad genes already, its normal. and our kids with a non relative mate will be a gamble bred in or out.
if 2 down syndrome kids unrelated made a kid, they still have a good chance of the kid being normal at birth.
if 2 down syndrome kids of relation made a kid, they WILL make a handicap baby.
but 2 related kids with no noticeable genetic disorders make a baby, you likely wouldnt ever even know.