Walmart can't even police (as in collect, contain, and put away) their shopping carts...think they can manage something with any semblance of a nervous system?
I don't go to Walmart unarmed anymore at all, specifically because of the people you mentioned in the first paragraph...and also a near incident I experienced myself while unarmed a few weeks ago.
Very few businesses, or government agencies for that matter, have someone dedicated to monitoring security cameras (CCTV). And even those that do are not reliable due to the fact a human can not watch a CCTV monitor showing parked cars or empty aisles for more than 30-45 minutes without a serious degradation in concentration.
If you are anywhere that has security cameras, do not think someone is watching over you. But that fact is really not much different from the police. You would like to feel they are out there to protect us, but they are becoming more and more uniformed crime scene investigators, coming to help AFTER THE CRIME.