The problem here is the authority of the agency. The '68 GCA is outright unconstitutional - it prohibits people from selling Constitutionally-protected property to others across state lines (you have to go through a "dealer"), it prohibits you from dealing directly with manufacturers (just try buying an AR clone directly from Bushmaster, DPMS, etc., or a handgun from S&W, Springfield, Glock, etc. - it won't happen unless you have an FFL) and it allows the agency to ban whole classes of guns from civilian ownership under the unlimited, undefined, unconstitutional and unreviewable standard of "sporting purpose" (which, by the way, was a concept lifted directly from the 1938 Nazi Weapons Law - see http://www.jpfo.org/GCA_68.htm ).
BATF abuses got the '86 FOPA passed, which forced BATF to ease up a bit, and which allowed interstate shipment of ammo and protected interstate travel with long guns. Maybe the abuses now being testified about can bring some more changes for the better.
You didn't even mention the original federal gun control law. The National Firearms Act. It was for violations that act, not GCA '68 or any other "law", that folks were killed at Ruby Ridge (too short) and Waco (alleged machine guns). It's just as unconstitutional as the others. It's alos the only one to make it to the Supreme Court, in a cast which was sent back to the lower court for "further action", which could have been anything, from reinstatement of the charges, to further pleadings and evidence that a short barrelled shotgun did have militia/military usefulness. The machine gun provisions, the associtated tax, and registry, have never been tested at the Supreme Court.