As a child I was always told that "ignorance of the law is no excuse" and it wasn't until I grew up that I realized the fundamental offensiveness of such an approach to law. The ancient Common Law principle of mens rea stands in opposition to such tyranny.
Mens rea is Latin for "guilty mind". In criminal law, it is viewed as one of the necessary elements of a crime. The standard common law test of criminal liability is usually expressed in the Latin phrase, actus non facit reum nisi mens sit rea, which means "the act does not make a person guilty unless the mind is also guilty". Thus, in jurisdictions with due process, there must be an actus reus accompanied by some level of mens rea to constitute the crime with which the defendant is charged. As a general rule, criminal liability does not attach to a person who acted with the absence of mental fault.
The modern proliferation of laws, rules, and regulations -- often created by bureaucrats and not elected officers -- makes it impossible for people to know the boundaries of legality, thereby putting every person in peril of accidental criminality. Even people who ask government agencies for clarification are out of luck.
It has thus become impossible for an ordinary citizen to know what is legal and what is not. In fact, as anyone who has ever tried to assure his or her legal safety by asking for guidance from the IRS or EPA knows, the agencies themselves don't have a clue, and are prompt to disclaim any immunity to prosecution for actions based upon their own advice.
I've experienced this. When I called the IRS for information about how to fill out a tax form I asked if there would be any record of my call in case I was audited after following their advice. The lady just laughed and informed me that "the IRS told me to do it" is no defense.