i think that the main problem is that they DO ultimately want to ban all one-handed opening knives, then they can start on all folding knives next. today assisted opening, tomorrow ones with thumb studs, the day after the ones with....
by setting a precedent that an agency like the customs can effectively make it's own laws by redefining the semantics in defiance of previous judicial case history and judgements, we are going down a slippery slope. it's the death of a thousand cuts by stealth rather than a more obvious law passed by congress, or even an executive order. once you start allowing customs to make up regulations based on partisan political considerations you're stuffed, they already have their foot in the door...
customs of course only is involved in the foreign import/export of these items, but if they get away with it, what's to stop the post office or other agencies. of course the mfg. who currently import such things could set up a factory inside the U.S. to make them, creating more non-outsourced jobs. OSHA or some other agency would probably then ban them by regulation.
the price of freedom is eternal vigilance