I believe a lot of the problem comes from de-humanising the wearer.
We gain a lot of information through watching the face of a speaker*, which I would hazard to guess is very important in a trial situation. Religion aside, would it be acceptable for me to turn up to a trial and give evidence while wearing a motorbike helmet?
I would hope/imagine that for the judge to consider the trail ‘fair’ then she will have to remove it while speaking, if nothing else to make the trial a level playing field (so to speak).
At the end of the day this is a democratic state, not a religious one. Because of this my understanding is that the law takes precedence over religion, but do correct if wrong**.
*This is why I am constantly misunderstood on this forum – *sigh*
**As I am sure it will be.