Help applying Mill's harm principle to a contemporary case

I'm sure most of you are familiar with the harm principle laid out by Mill in his essay On Liberty which states that society may coerce an individual only if his opinion harms others. I'm curious how this priciple would be applied to a situation I saw on the news recently. A judge in Alabama was dismissed for wearing the Ten Commandments on his robe. Would Mill, relying on his harm principle, think this was the right thing to do? I think he would say yes, for a judge is supposed to enforce the secular laws of the state, and by basing his judicial decisions on the Ten Commandments instead, he could very well harm others.
Some difficulties arise, though, because the secular laws and the Ten Commandments often lead to the same conclusions. Therefore, reliance on the Ten comandments would only harm those that come before the judge some of the time instead of all of the time.
What's your opinion? Did I apply the principle correctly, or should the judge have not have been fired? Also, a person could hold the opinion that the Ten Commandments should take precedence over secular laws as long as that opinion didn't harm others; so someone who was not a judge would be allowed to hold this opinion, right?