Unlike Russell Moore, head of the Ethics and Religious Liberties Commission, I wholeheartedly commend the actions of the Alabama Supreme Court. Note too that Judge Roy Moore is so concerned for even the appearance of fairness that he recused himself, a concern for scruples utterly lacking in a couple of US Supreme Court justices that come to mind.
If the federal judiciary were to declare that state laws limiting marriages to two persons concurrently was a violation of the civil rights of persons who were polyamorous in orientation (which, incidentally, is the logical follow-up to denying the primacy of the duality of the sexes), the states would likewise have the right to ignore such rulings.
If the federal courts were to rule that children have all the same rights as adults (as regards sexual intercourse, entering into marriages, voting, access to alcohol, employment, etc.), the states would likewise have the right to ignore such rulings.
If the federal courts were to rule that people have a right to marry a consenting adult who just happens to be a close blood relative, the states would not only be justified in ignoring such a ruling, they would be morally obligated to do so.
The federal courts have no unlimited right from the Constitution to legislate.