It is commonly said that "Ignorance of the law is no excuse."
The reason why this is so is that when that precept was first formulated, common sense and the law had a lot in common. That meant that when faced with a choice of doing something, you could consult your common sense and use it to decide whether to do something, and odds are, that would tell you if it were legal.
In this era, you could literally spend the rest of your life reading laws that you are theoretically being held to at the federal, state, county, township, city, and if you like, international level. Even lawyers can only specialize on a small aspect of a particular level of law. Common sense and the law are no longer so intimately related that we can use one to reliably determine the other.
Therefore, ignorance of the law should be accepted as an excuse. There is no plausible way anyone can be expected to know all the laws applying to them, and it's getting worse. Holding people responsible for things they can't even guess at is not Justice.
I'd turn this into an essay, but really, what else is there to say?