If you've ever been to a law library and seen the  hundreds, probably thousands of books you logically would know that ignorance of the law is a valid excuse.  To say otherwise is to assume that in a lifetime, while going to school, working and raising a family one could actually read all those and remember them.  Even lawyers come to court and are surprised by some segment of the law of which they were unaware.

I was in the basement which held the law books of local attorney and was astounded.  However that library paled in comparison to the one at the Lyndon Johnson library (which you aren't allowed to photograph.)