Are the TSA rules legally binding?

At the end of the day, the question boils down to "Can you be arrested or fined for trying to bring banned items on board?", and the short answer to that is "No", unless you're trying to bring in weaponry or getting uppity when busted. Straight from the horse's mouth:

TSA recognizes that most passengers who carry prohibited items do so without any ill intent. TSA does not impose fines on the vast number of passengers who inadvertently carry prohibited items. Dealing with any prohibited item, however, adds time to the screening process both for the traveler who brought the item and for other travelers as well. Some items pose such a risk to the traveling public and the screening work force that TSA will consider imposing a fine on the traveler.

Items for which fines may be imposed include firearms, ammunition and other explosives, incendiaries including larger amounts of self-defense spray, and certain dangerous knives. Fines also may be imposed when passengers attempt to artfully conceal prohibited items or behave in a manner that is so uncooperative and disruptive that it physically interferes with the screening process. Carrying some prohibited items could result in both a civil and criminal enforcement action.

Basically, violations of TSA regulations can lead only to civil charges, not criminal ones; you cannot be arrested or thrown in jail for breaking them. There are only two caveats: one, they'll happily dob you over to the regular cops if you actually do something criminal like punching them, and two, there are some things like heavy weaponry (but not 4-oz bottles of water) that are banned by criminal law as well.