Twins Marry by Mistake

A MARRIED couple have had their union annulled - after discovering they were twins.The twins were separated at birth and not told they had any siblings. They were adopted by different families, and - amazingly - as adults they met, fell in love and married.The High Court ruled the marriage had never been valid and annulled it.http://www.thesun.co.uk/sol/homepage/news/article677584.ece 

So now the question begging to be asked is If same sex couples can marry then why not siblings?

We’re constantly told that it’s “not fair” to deny people w/ same sex attraction the “right” to have sex and marry those they “love”. These 2 people (the twins), not knowing they were related, fell in love and are obviously sexually attracted to each other. How is it “fair” to deny them sexual relations and all the benefits of marriage? Afterall, they aren’t going to be able to just turn off their feelings or desires, just because a judge ruled their marriage invalid, and the law says sexual relations b/t them is illegal. Sure, their offspring could have serious genetic problems, perhaps making their relations unfruitful. So they can adopt, or do artificial insemination or IVF. JUST LIKE GAY COUPLES. There is no difference. You can’t have it both ways.