I am a little mystified as well, especially the part about not being able to determine "criminal intent," as I thought the overriding principle to be ignorance of the law is not an excuse.

The general rule under common law is that "ignorance of the law or a mistake of law is no defense to criminal prosecution."[12] In some cases, Courts have held that if the law is extremely complex, such as a tax code, a defendant may use ignorance as a defense to willfulness if his misunderstanding is in good-faith:

The proliferation of statutes and regulations has sometimes made it difficult for the average citizen to know and comprehend the extent of the duties and obligations imposed by the tax laws...the Court almost 60 years ago interpreted the statutory term "willfuly" as used in federal criminal tax statutes as carving out an exception to the traditional rule."[13]

Crimes like tax evasion are specific intent crimes and require intent to violate the law as an element of the offense.[14] Not all offenses require specific intent, and a misreading, even in good-faith, may not excuse the criminal conduct.[15] A good-faith belief that a law is unjust or unconstitutional is no excuse,[16] but "reasonable compliance upon an official statement of law, afterward determined to be invalid or erroneous" does not constitute a criminal act.[17]