Yep once gays are given the right then brothers and sisters will demand the same rights to marriage.
Ah yes, maybe all 20 people who want to marry their sister in the United States?
I can't think of a topic that is less important or less relevant....
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No one knows how many brothers and sisters have had sex and love each other beyond brotherly and sisterly love. But once you open the door you will find out.
Doesn't matter, because the legal standard is different.