Thank you for posting that BC1 because it does make for interesting discussion.
Why did Walgreens hire an armed security guard to begin with? Would they waste their money on an armed security guard if they did not see a benefit to it greater than the outlay of cash to pay for it (unless the government made them do it)? I can see two reasons for paying extra for an armed security over more passive and cheaper security such as cameras, alarm systems and unarmed security. One is that it made customers feel safer and they would pick Walgreens to do business at rather than a competitor. Or that the presence of a visibly armed individual would cause the criminal to pick their competitors to rob or commit other crimes at. My supposition, which I admittedly have no evidence to back up, is that Walgreens felt they needed armed security as a deterrent to the criminal with the secondary reason being the added benefit of making customers feel safer to shop there.
Now, to the real meat of the discussion. Your post illustrates that there are no absolute in life, only odds. To me, carrying a firearm in everyday life is like playing poker with 4 kings and a joker. Does holding 4 kings and a joker, hidden from the other players, completely by itself, do anything to keep the other players from betting against me? Well, if you take into account that it denies them the kings and joker, maybe a tiny little bit - but not really all that much. The hidden cards can't do anything to keep the other players from betting against me, although there may be other tell tale signs that I might give off that they don't want to bet against me, but I can also give those tell tales signs without holding the 4 kings and joker. The 4 kings and the joker, hidden from the other players, only very greatly increases the odds that I will win the hand. And that certainly is a very good thing.
But, what if I am dealt 4 kings and a joker and immediately show all the other players what I have? What have I done? I have very greatly decreased that chances that anyone will bet against me. When dealing with criminals and protecting my family, my number 1 goal is to prevent the criminal from ever attacking me to begin with, my number 2 goal is to win the fight if they do choose to attack. If I show that I have been dealt 4 kings and a joker, does that completely eliminate those that will bet against me? No, it doesn't. There might just be that guy that has 4 aces and the other joker. There might be that guy that wants to try to bluff me and make me think he has 4 aces and the other joker. There might be that guy that just wants to lose it all anyway. But the odds that nobody will bet against the 4 kings and joker that I show them far, far, many times outweigh the odds that someone will even bet against me to begin with.
I know that my openly carried firearm won't keep every criminal from attacking me. But there are no absolutes in life, so I don't count on absolutes - I play the odds. And, of course, location and environment affect the odds as well - if you are playing poker with two decks of cards, the 4 kings and joker only have 1/2 the chance of winning the hand. But in my environment and my location, I don't really have to worry all that much about their being two decks of cards because I don't live in a gang infested, high crime rate cesspool.