Sorry, charlie. There's a compelling state interest served by bans on marriage between close relatives. You see, procreation between close relative produces a demonstrably higher incidence of birth defects and mental disorders. The same cannot be said of same sex unions.Yea, for the same reason a brother can't marry his sister or a man can't marry his daughter. It's illegal.
Can you indicate a compelling state interest served by denying same sex couples equal protection of the law to marry? I bet you cannot even indicate a legitimate state interest served by doing so.