Ideally there would be no restrictions on what side arms you can carry whether it's a pistol, dagger, sword, or whatever.
In Michigan it's illegal to use any knife with a blade over three inches long
against another person with unlawful intent to harm them. I think unlawful intent is assumed by a lot of cops, or, like many other laws, they just don't know what the law is. I just read that switchblades are legal in Michigan since last October, but there are still too many restriction on knives.
A person shall not carry a dagger, dirk, stiletto, a double-edged non-folding stabbing instrument of any length, or any other dangerous weapon, except a hunting knife adapted and carried as such, concealed on or about his or her person, or whether concealed or otherwise in any vehicle operated or occupied by the person, except in his or her dwelling house, place of business or on other land possessed by the person.
I could carry a hunting knife while hunting, but couldn't transport it in a vehicle. Where I used to hunt was a 2 hour drive away. So, it's a helluva long walk to the hunting grounds, and I better not get stopped along the way.
Michigan law prohibits a person from carrying a dagger, dirk, stiletto, or a double-edged, non-folding stabbing instrument of any length. The prohibition on “double-edged non-folding stabbing instrument of any length” means that, although automatics are now legal, an out-the-front double edged automatic would be prohibited under the amended statute. A double edged spear point knife cannot be carried in Michigan. A spear point knife with an unsharpened false edge is not technically double-edged, but it might be classified as a dirk or dagger by a prosecutor.
The way the old law was written spring-assisted knives were illegal too. It looks like the new law doesn't apply to gravity knives. A long time ago I wanted a German paratrooper gravity knife, but didn't want to go to prison for a felony offense. Under the law they must be seen as more dangerous than switchblades. This needs to change. I still want one.
https://german-knife-shop.com/product/eickhorn-rt1-tac-ll80-paratrooper-gravity-knife/