Let me start by saying that I don't think this should have ever gone to court. It is a worrying precedent and will be a negative for self reporting and flight safety.
However......
I don't see the grey area. There is a curfew. Everyone knows the rules down there. They aren't new. It is black and white. After xx:xx, you cannot take off. Park the jet and go to the hotel. All the other factors in this incident could be argued but this one is indefensible. Does it deserve a court case? Probably not. Just culture should apply. Did he knowingly break the rule? If so, why?
As for "command prerogative/authority", call it what you will. It is largely a myth. The only time a PiC can intentionally ignore the law is if following it would be the more dangerous situation. You cannot use the so called "command authority" to ignore the law, just because you judge it to be safe, or in the company interest, or you want to get home or whatever.
When I got my first job I was told the following to aid in decision making:
1)Is it safe?
2)Is it legal?
3)Is it in the companies interest?
If you can satisfy ALL THREE, then go for it.