It matters quite a bit. Go back and take a look at the can of worms Roberts opened up. It’s all about ignorance of the law being OK as long as you’re in “authority”. Such an opinion goes way beyond the circumstances here.
I understand perfectly what you are saying and I was only commenting on stopping someone for a traffic violation. I wonder if we -the peons - can now claim ignorance of the law as a viable defense? Hmmm, probably not -