"Advisory Circulars are neither binding nor regulatory; yet some have the effect of de facto standards or regulations." Therein lies the contradictory hook, my friend. "De facto" means, though it is "neither binding nor regulatory," in fact, it may be treated as such and have the import and force of law. Personally, I think such "de facto" applications violate Due Process under the Constitution because citizens can not be held accountable for equivocal laws. Due notice of what is against the law is an inherently integral part of due process. You can't tell an American citizen it is not "advisable" to go through a red light when there are no laws prohibiting it and then fine and/or otherwise punish somebody who doesn't stop for a red light simply because an agency "advised" against it. Am I making this concept clear or just muddying things further for everybody? Bottom line, the FAA has virtually unlimited litigative resources, so unless you are Bill Gates, it is an unfair David versus Goliath proposition.