Supreme Court Justice Sonia Sotomayor said it this way:
Sotomayor asked, "If you say that marriage is a fundamental right, what state restrictions could ever exist?" before referencing "polygamy and incest among adults," as reported by Matt Canham of the Salt Lake Tribune. The argument is an illustration of a broader issue about the culture of American society. To agree that gay marriage is indeed protected by the "equal protection" clause in the Constitution, wouldn't the same apply for all consenting adult relationships?
Justice Sonia Sotomayor: If Gay Marriage Is... | Gather
Depends.
1. Just because I have a consenting adult relationship does not mean that the other adult I'm in that consenting relationship with decide to go to the step of marriage. There are many relationships that are not marriage. For example I have a friend and I give her a power of attorney to sell my car while I'm overseas for a year. That is a consenting adult relationship, but I didn't need to Civilly Marry her to do it. On the other hand Civil Marriage is a contractual relationship between two consenting adults to establish a family relationship where one did not exist before - which is a whole different level.
2. Secondly, because Civil Marriage between same-sex couples becomes acceptable extending Civil Marriage Equality, that does not mean that other types of consenting adult relationships must automatically be acceptable under the law. Ultimately there will be an examination of that relationships structure and a determination made as to whether there is a compelling government interest in recognizing such a relationship under the law. If there is a compelling government interest in withholding legal recognition - then it will not succeed. The problem that those that wish to discriminate against same-sex couples have is that there is no compelling government interest in treating law abiding, tax paying, US citizen, infertile, consenting, adults differently based on gender in terms o Civil Marriage couples.
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