Prop 8 was overturned (in the case of California only) because ...
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The people may not employ the initiative power to single out a disfavored group and strip them, without a legitimate justification, of a right as important as a right to marry.
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Nothing changes right now - the Mormons and other pro-Prop8 backers have the right of appeal. It has to be them, since the State will not support it. And California is a unique case, because the State Constitution was found to allow Gay Marriage - which was taking place - when the initiative process took away that right.
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But it is nice to know that the court doesn't think it is acceptable to single out a group to legislate against just because you don't like them.