Well if there were a crazy person about to try to shoot everyone in a Kroger store, I would be happy to know he had company in carrying his gun into the store.
In the little town I grew up in, we didn’t think anything of it if we walked into the story carrying a shotgun on our way to the woods. The same was true of every other business there on Main Street and that was well into the 80s.
Just as a note, I don’t believe that there is a single supermarket (of any brand) by the normal definition of “supermarket” in Detroit.