In fact the judge that made the law to remove the religious icon was prohibiting the free excercise of said religion and abriding the freedom of speech. Which in my view can be seen as Unconstitutional if you ignore the fact that the Constitution only limits Congress and not the judicial system. It does not say The Government, it just says Congress. Show me where Congress passed such a law. It is a loophole and States, Cities, Courts can pass laws that are not limited as Congress is. Either the Constitution needs to be amended, or the rulings made fall out of the juristiction of the Constitution because it limits Congress and not other parts of the government.
I think what you are missing is that the court room is not the judge's property. The court room belongs to the state, and the state (under current judicial theory*) is bound to follow the Constitution.
Of course the state does not pass individual laws to specify how government buildings are decorated, rather they deligate the authority to handle that to somebody. But that person is still bound by Constitution, because the state can not authorize somebody to do something that it can not do directly.
Putting more simply, when somebody decorates a court room, they are doing so because a law authorizes them to do so. That law, and by proxy anybody implementing it, is bound by the Constitution.
Jay
* The idea that states are bound to follow the Constitution is called incorporation and that is a matter of much judical wrangling. Personally I think incorporation is valid, but that it has been rather selectivly applied on occasion.
Jay