The liberal logic here is inescapable. Since crimes like this have occurred then this type of crime is foreseeable. If the crime is foreseeable then owners of private property are liable. In order to eliminate that liability private property should be eliminated. The crimes will continue but since all property will be gov. property no one will be liable for it. Problem solved!
These businesses are consciously considering the question, if a shooter starts shooting up the place, do we want any of our patrons to be armed?
By declaring know, they have unreasonably put their patrons in more danger.