W. MITCHELL NANCE, a family court judge in Kentucky, has enfolded himself in a cocoon of principled self-righteousness by declaring that, “as a matter of conscience,” he will refuse to hear any adoption cases initiated by gay or lesbian parents. The judge is entitled to his opinions. However, having declared his unwillingness to enforce the law and his open prejudice against an entire class of Americans — including litigants who may bring other cases before him — he is not entitled to remain on the bench.

The law of the land is clear. The Supreme Court ruled in 2015 that same-sex marriage must be permitted in all states. Kentucky, like every one of the 50 states, allows adoption by gay couples. What Mr. Nance regards as “a matter of conscience,” then, is in fact in direct defiance of settled law. If a judge cannot accept the law, and in fact is, by his own account, incapable of impartial and fair adjudication of that law, he is, as “a matter of conscience,” duty-bound to seek a new line of work.

There are widely accepted criteria by which judges can and must recuse themselves; the conviction that the law itself is illegitimate is not one of them.

A judge should recuse himself if he or an immediate family member has a personal interest in a case, by dint of financial, personal or family relationship. He should recuse himself if he is plainly biased against one or the other party in a case that comes before him in a proceeding. Bias against a whole slice of the population is a different, and disqualifying, matter, and renders Mr. Nance unfit to serve.

The law does not tolerate discrimination based on race, religion or sexual orientation, but Mr. Nance does, by his own admission. He acknowledged to a local journalist that homosexuals might have legitimate reservations about appearing before him, which they might in custody or divorce cases, among other proceedings.

The judge is as heedless of fact as he is of his duty. In a written order explaining his blanket recusal, he wrote that “under no circumstance” would the best interest of a child be served in an adoption by a “practicing homosexual.” In fact, the vast bulk of research shows that children adopted by gay parents fare as well as those adopted by heterosexual couples.

Mr. Nance’s stance is akin to that of Kim Davis, the Kentucky county clerk who, on religious grounds, refused to issue marriage licenses to same-sex couples following the Supreme Court ruling that they must be allowed nationwide. In Ms. Davis’s case, her so-called conscientious objection was rendered moot by legislation in Kentucky that scrapped the requirement that county clerks sign marriage licenses. In Mr. Nance’s case, no such work-around is possible or justified. Family court judges must hear adoption cases. And if Mr. Nance cannot fulfill that duty, he is no longer equipped to do his job.