The evidence was irrelevant, the judge rules on evidence every single day in our courts. The Marines may grant permission or deny permission. Provide an example of something that must be allowed without permission.
No denying that. My question is why was this Marine supposedly singled out. My take, again, is that she was a problem child, and had deeper issues and was trying to hide behind religion.
That being said, even though this is the Marines, and what an NCO says to do, if lawful, should be followed, if said NCO allows other Marines to do what this one Marine is denied, then there is an issue. Especially something as mundane as workstation decorations.
Want to make it stick? Then ensure all workstations have no personal items on them. Problem solved.
When I was stationed at Osan Air Base, Korea, back in the late '80s/early '90s, we had several black Airmen who were wearing "Black to the Future" or "Black Power" t-shirts on base while off duty. Imagine the furor if a white person did the same. Base commander said all shirts of such type were banned on base, for all races/ethnicities. Problem went away, and no one could say "boo" about it.
So no, I don't think this issue was about religion, I do think it was about a problem child, but the Marines could have helped themselves significantly by ensuring no one had any personal items on their workstations. Period.