I just don't really see the point why civil society would want to encourage concealed weapons except for undercover law enforcement or something. . ..
I'm not advocating it, but I wouldn't be surprised if the argument is something like "well a criminal then doesn't know who is packing and who ain't, and may be less likely to commit crimes in person".
Either that or when people see someone packing, they kind of freak out, so it's better not to know it's there.