While I don't necessarily agree with, say, sibling marriage, the argument about birth defects is not very compelling. This ruling pointed out at one point that an ability to procreate is not a requirement for marriage in any state. Further, genetic testing to avoid birth defects is not a prerequisite for marriage, so why would sibling marriage be precluded to avoid birth defects. Should society therefore only allow siblings or cousins of the same sex to marry because they can't procreate?