The US had a thriving switchblade industry until 1958.
The Switchblade Act, (public law 85-623, enacted on August 12, 1958, and codified in 15 USC 1241-1245), prohibits the manufacture or transportation of switchblade knives in interstate commerce. It provides exceptions for government agencies, members of the Armed Forces, and for one-armed persons.[10] The act was amended in 1986 to also restrict ballistic knives. 18 USC 1716 further restricts sending switchblade knives through the United States Postal Service, with a few exceptions.
Take a look at the Wikipedia entry:
http://en.wikipedia.org/wiki/Switchblade
There are no Constitutional rights protecting knife ownership.
With the pocket clip, assisted opening and waved knife designs switchblades became a collector and novelty knife. These other designs offer hard users more accessibility, utility and reliability.
A switchblade that isn't locked in your pocket is liable to fire by accident. A locked knife requires yet another action to bring it into use. You can't use a switchblade until you dig it out of your pocket and clear your body. You have to find the button, make sure your clear of the opening, press it, forgot to take off the safety, take off the safety, press the button and assume a good grip, that is if the knifes spring action doesn't flip the knife out of your hand,
Compare to a waved knife, clipped to your pocket, grip the knife drag it up the back of your pocket and at the end of the action you have a live knife in a secure grip.
Of course there's Frank's Guntling which works well even when closed, using it's special design features to control, scrape and scratch even opening the blade. A great martial arts knife.