Responding to "Homosexuality is wrong, the same way incest is wrong"

[Losty]

Wouldn't a consistent application of that logic also preclude, say, handicapped people from having children, where that handicap is inheritable? Where do you draw the line, in terms of what's an acceptable likelihood of genetic defects?

For me there is a difference between potentially passing on a genetic defect that one or both parents have, and potentially creating one.

If two otherwise healthy adults who are directly related have a significant chance to create a child with mental retardation or other defect, I would say a line could be drawn.

It doesn't create anything new. It increases the risk of inheriting recessive genes. It will hurt a society if done over generations. The increased risk in a single case of incest isn't nearly as high a risk as 2 people with a hereditary disease having a child.