Part of the problem is that most people haven't a single clue what state or municipality laws are in force -- or especially "not" in force in their area. While in the National Guard in Idaho, I worked with a guy who was a Boise City cop. He was visiting in my office while I was opening my mail with my BM AFO. He jumped up, freaked out, and told me that knife was illegal in this state and I was presuming on our friendship if I continued to use it. Without saying a thing, I opened up my briefcase and took out a copy of the various idaho codes about "weapons" which indicated absolutely no laws pertaining to automatic knives. He couldn't believe it and told me he would make it a personal issue to find them and report back to me the next week. Sure enough, we got back together later and he had to admit he'd been wrong. So if the cops are wrong on this issue, it is equally understandable that most people are also wrong.
...and then in the more mobile age we live in where you may be born in one place, raised in another state, and your career takes you to the other side of the country, one sometimes tends to think laws are the same in all states. They aren't! Automatics are unlawful here in Washington State wher I moved from Idaho about a year ago. They are perfectly legal in Idaho and Utah (where I grew up). No one bothered me during that portion of my 23 years of military service that I carried an auto. ...but on deciding to move to Washington for a job promotion, I gave my BM AFO to a Special Forces Captain I know who took it to a "classified country" and is still using it there even today!
Bruce