"You weren't there."
Well, in all legal cases, the people deciding the verdict (either a jury or the judge) weren't present at the scene of the crime either, but they have a very refined way of determining guilt or innocence. It's called evidence. I dare say any Christian accused of a crime would expect evidence exonerating him or her to be presented in court and duly assessed by the jury or judge, or if they are the plaintiff, to expect that evidence that they have for the commission of a crime against them would be duly heard and evaluated.
If they had an evidence-based alibi that they were somewhere else other than the crime scene they would rightly never accede to someone saying, "Well, I have this magical book that claims itself to be correct that if interpreted in the proper way shows that the defendant is guilty. And since the jury wasn't there, my version is just as valid as the defendant's." Well, no it isn't as good.
Science has evidence that exists in the real world that anyone can examine and that's the same for everyone, apart from anyone's opinion. Religion has nothing except personal testimony and florid rhetoric. You wouldn't accept what passes for arguments by theists in a court of law and you shouldn't accept it for arguments about morality or any other "ought" we need to consider.
By the way, this is why creationists lost in the Dover case. In a court of law, facts matter.