Should have never been illegal in the first place. If it wasn't for senator Estes Kefauver showboating in the Senate with a huge display style stilletto, mis-representing them as the type gangs used, they would have never been illegal.
I tried to guess why automatic knives are illegal in so many places, and the best thing I came up with is because they are accidents-prone. An out-the-front automatic knife is more likely to accidentally engage than an assisted opening model. This could be dangerous for the carrier if the knife is put in a pocket or backpack and accidentally engages with enough force to penetrate through clothing and skin. I don't know much about automatic knives, but does that sound reasonable to you guys?