In the first place, a 5–4 Supreme Court decision counts as a Supreme Court decision. The decision isn’t invalid just because it wasn’t unanimous. So let’s get that ridiculous argument out of the way.
Next, the states do have the right to set up their own rules and regulations regarding marriage — BUT they must do it without discrimination. If they allow white people to marry, they must allow black people to marry. If they allow Christians to marry, they must allow Jews to marry. And if they allow heterosexuals to marry within their sexual orientation, they must allow homosexuals to marry within their sexual orientation.
States have always created their own rules for marriage. You say that interracial marriages are different from same sex marriages, in that extra wording needs to be added to prevent them. However, for over a century, marriage was defined in a number of states as a man and a woman of the same race. Nothing was “added” — that’s how marriage was defined, until the Loving decision changed that. States have varying rules about the minimum age at which a person may marry with parental consent, and a minimum age at which a person may marry without parental consent, and this varies from state to state. Some states allow one to marry their first cousin, and other states don’t. And as long as these rules apply to everyone equally, they can do this.
If a state decides not to allow anyone to marry at all, they could technically do that, and gays would not be allowed to marry. Of course, neither could straight people. And any state politician supporting a universal marriage ban isn’t going to get re-elected.