First, the idea that "you can't shout fire in a crowded theater" is from a now discredited Supreme Court case that excused the jailing of a citizen for the "crime" of handing out pamphlets opposing the draft during WW 1. It is much, much harder to prove culpability for words, even in tumultuous contexts, these days.
Second, the idea that we let off soldiers and policemen -- and the Nazis after WW 2 -- because "they were just following orders" is nonsense. We hanged and shot people after the war for following certain orders. And in the US military today, our uniformed personnel are repeatedly told that you can be tried for following an illegal command.
These two mistaken tropes illustrate a larger problem. When we're sure of the moral dimension of our case, we throw all kinds of brickbats against it. Any stick will do to beat a dog, as the old saying goes. But if we want to build a better society, it matters what arguments we use to advance our cause.
Let me give you an illustration of the wrongheadedness of citing ignorant misunderstandings of the law.
Years ago, I had a parishioner call me, and very upset she was. Her nephew had announced plans to marry his first cousin, once removed. Citing the frequently misunderstood idea that the child of your first cousin is your second cousin, he and his intended had obtained a marriage license for that purpose. Regardless whether her nephew cited the mistaken belief that his bride was actually his second cousin because of ignorance or fraud, the license wasn't valid. My parishioner wanted to forewarn me in case they came looking for me to marry them.
Well, I wouldn't have married someone who just appeared, license in hand, under any circumstances, but I thanked her for the heads-up. The lovebirds found someone, though, to do the deed: a self-appointed minister without a church of his own. They rented a vacant chapel down the road, and there the wedding took place. When the "minister" was tasked with having married a couple not permitted to marry under the laws of Indiana, he scoffed, saying, "They do that all the time in Kentucky." Well, actually, no they don't. Kentucky law is the same as Indiana's in that regard. And even if it had been otherwise, they didn't have a Kentucky license.
So: if I assert, whether from ignorance or fraud, that my first cousin, once removed, is actually my second cousin in order to obtain a marriage license, does that make my marriage valid? If I conduct an illegal marriage because I ignorantly assume that it's okay somewhere else, does that excuse my conduct? If lots of people believe both these ideas (and they do), does that make either of them more excusable?
No. No. And, no.
We live in an age where people believe whatever they want, and think that their belief creates a different reality as regards the law. Even scarier, they are willing to believe contradictory things at different times, in order to argue for or against a particular person or cause. The result is that ideas are drained of their meaning. If all that matters is what side somebody is on, then the whole idea of the rule of law itself has no meaning.