A federal district judge in Idaho has issued a ruling striking down the state’s law banning same-sex marriage:

Gay and lesbian couples in Idaho could start getting married as soon as Friday after a judge ruled the state’s ban on same-sex marriage is unconstitutional.

U.S. District Magistrate Judge Candy Dale wrote in her decision Tuesday evening that Idaho’s laws barring same-sex marriage unconstitutionally deny gay and lesbian citizens their fundamental right to marry. Ten other federal district courts have issued similar rulings supporting gay marriage rights.

Dale said the state must issue marriage licenses to same-sex couples starting at 9 a.m. Friday….

In addition to Idaho, federal or state judges in Oklahoma, Virginia, Michigan, Texas, Utah and Arkansas have recently found those state bans to be unconstitutional. Judges have also ordered Kentucky, Ohio and Tennessee to recognize same-sex marriages from other states.

The full text of federal Magistrate Judge Candy Dale’s opinion is available here.

As the AP story quoted above points out, this is just one of many federal and state judicial rulings striking down laws banning same-sex marriage issued since the federal Supreme Court decided United States v. Windsor. I previously blogged about similar decisions by federal trial courts in Texas, Virginia, ad Utah, as well as a state supreme court ruling in New Mexico.

When Windsor came down, I predicted that it would give a boost to efforts to strike down state laws banning same-sex marriage. But I honestly did not expect them to achieve this much success so quickly. What is striking is not just that numerous courts have issued decisions striking down same-sex marriage bans, but that opponents of same-sex marriage have yet to win one of these cases since Windsor. This is a strong indication that supporters of same-sex marriage have the momentum. We might well see the issue return to the Supreme Court in the near future.

The Idaho decision strikes down the state’s ban on same-sex marriage based on the theory that it violates the “fundamental” right to marriage, which is subject to strict scrutiny under the Due Process Clause of the 14th Amendment, and also because it constitutes discrimination on the basis of sexual orientation, in violation of the Equal Protection Clause. In my view, these rationales, especially the first, are not as strong as the argument laws banning same-sex marriage violate the Equal Protection Clause because they discriminate on the basis of gender. Judge Candy Dale, however, rejected the sex discrimination claim on the following grounds:

Idaho’s Marriage Laws allow heterosexuals, but not homosexuals, to marry and thus clearly discriminate on the basis of sexual orientation. This distinction does not prefer one gender over the other—two men have no more right to marry under Idaho law than two women. In other words, Idaho’s Marriage Laws are facially gender neutral and there is no evidence that they were motivated by a gender discriminatory purpose.

Judge Dale is simply wrong to suggest that Idaho’s marriage laws are “facially gender neutral.” To the contrary, as she herself summarizes elsewhere in the opinion, they explicitly limit marriage to opposite-sex couples, which means that the range of people whom Idahoans are permitted to marry is defined by their gender. Article III, Section 28 of the Idaho Constitution states that “A marriage between a man and a woman is the only domestic legal union that shall be valid or recognized in this state.” Section 28 defines legally recognized “domestic unions” purely based on the sex of the participants, not on their sexual orientation. If they live in Idaho, Anne is allowed to marry Bob, but Charles is forbidden to do so even if the only difference between him and Anne is that one is a man and one is a woman. A situation where your legal rights depend on your gender is the very essence of facial sex discrimination.

By Judge Dale’s reasoning, a law banning interracial marriage might be considered “racially neutral” because it “does not prefer one race over the other.” Under such a law, blacks have no more right to engage in interracial marriage than whites, and vice versa. Dale’s reasoning replicates a similar error made by the Supreme Court of New Mexico in December. That mistake was avoided by the federal district court that recently invalidated Utah’s ban on same-sex marriage.

I think Judge Dale ultimately reached the correct conclusion, even if she didn’t based it on the best available reasoning. But the different rationales under which courts might choose to strike down laws banning same-sex marriage have divergent implications for future cases.