Therein lies the answer to why this case is about more than a threat to Christianity and more than just a threat to all religion.
... religion is being suppressed by the federal government of the United States in a manner inconsistent with our Constitution and History.
Religion and freedom of speech are being suppressed in this case but the key phrase is "a manner inconsistent with our Constitution and History". The Constitution is what is specifically under attack. Religion will exist whether it is legal or not. The Constitution only exists so long as its principles are understood and upheld. Those principles are consistently being undermined. Once the Constitution is rendered completely impotent and irrelevant it will be replaced.
If Algore had won the election in 2000 the principle of republican elective process would have been overthrown. That would have been severely crippling to the Constitution but not a death blow. The "Roy Moore/Decalogue" case cuts the Constitution off from its root, its initial authority, which was placed in an unamed God, "Our Creator." This was a completely non-sectarian reference to divine authority. Non-sectarian not just in the sense of divisions in Christian theology and not just in the sense of diverse religions but in a whole sense including non-religious and non-deist views. It was a placement of authority above and beyond man's will.
In spite of the fact that Judge Moore is a Christian and in spite of the fact that the Decalogue is the focus of this controversy neither Judge Moore, nor Christianity, nor God, nor the Ten Commandments is in any real peril here. Judge Moore demonstrated this on the personal level by refusing to deny his beliefs for the sake of a job. He lost his job but his core convictions remain untouched. God remains untouched. Christianity is untarnished by this. The Ten Commandments have in no way been altered by this.
The Constitution, however, has been severed from its root. Divine authority. Anything and everything it speaks to and protects is now up for grabs. There is only one replacement for divine authority among men; the rule of men. Those who seek to do this know that and want that.
I for one, a non-Christian, non-Jew, non-deist period do not want that. Without its root in divine authority over man's authority our Constitution is nothing more special than the constitution of the former Soviet Union. No rights at all just privileges of the State. The equality of men has rarely been surpassed as it was there. Religious man and atheist alike were equally subject to the brutality of statist authority. Defy the State on any issue there and the result was the same.
In spite of the imperfections of our Constitution, being instituted by men, and the erosions of its original intent and meaning over time by usurpers it is still the best invention yet created by men to prevent the tyranny of men over men. As long as it exists it offers some protection and has the potential to be perfected. It can only exist as long as it is connected to its ground.
China has millions of Christians. What it doesn't have is law to protect them ... or anyone else.