The arbitrarity of some states’ knife laws is also a problem. I don’t remember which state (OK pre ~2015 law updates perhaps?), but I read about one that had few carry restrictions below a certain blade size (somewhere in the neighborhood of 3 inches, IIRC), and if you’re caught carrying one over the limit, you basically have to give a specific purpose for having it. Assuming your case goes to trial, this means it’s more or less up to the judge to determine if your use was valid, which is juuuuuuuussst flexible enough to persecute the “right” people. (assuming I’m remembering correctly that this was in Oklahoma, that would be Native Americans)
Switching gears; Some More News had a pretty comprehensive video about moral panics, which also includes some history on switchblades in particular, for those interested.