[greggman]

Just a random thought but you could argue age discrimination is still equal because except for death, everyone goes through the same ages. In other words, when you're 25 you'll be treated by the law the same as other 25yr olds.

Brothers and sisters does seems to me like it's just people think of it as icky. Some cultures encourage marrying first cousins and the genetic risks are minimal. And even people that aren't related can and are tested for whether their genes combined will likely lead to genetic issues with their children. In other words the genetic risk is mostly not a valid excuse to ban siblings from marrying anymore than not being able to create children is for same sex couples.

[DanBC]

The risks are not "minimal". There are increased risks in cultures where first cousins marry. Part of that is that married first cousins have an increased risk of having children with birth defects. And part of it is that people are more related than they think if everyone is marrying a first cousin.

The link I posted earlier deals with this.

[anthony_romeo]

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?

[greggman]

Thank you for pointing that out but I still maintain it's irrelevant. People that will pass on genetic issues to their children are not banned from getting married nor banned from having children. On top of which as science progresses it's likely all those issues can be fixed. In other words, it's not a valid reason to deny siblings getting married.