I think the difference between “assisted open,” which is almost always legal, and “automatic open” (e.g., switch blades") is very minor. They are both just ways of freeing and locking the blade for use. I don’t think either of them implies they will be used as a weapon. I would guess the laws are just stupid and, as another user pointed out, related to a historical “moral panic.”
Damned greasers and their switchblades and leather jackets. When you’re a Jet, you’re a Jet all the way, from your first cigarette to your last dying day!