Who said that was his reason? From the experiences I have had and read about, the biggest reason businesses do not want open carry is that is upsets or makes other customers nervous, it causes a scene. I am not saying it's valid anymore than the danger argument but they would rather lose a single customer than have a store full of upset customers who start calling the police, this is how many look at the situation.
Note definition number two... of rationalization...(not critizing you, but using your post as way to make another point)
1.
process of rationalizing: the process of rationalizing something, or an instance of rationalizing something
2.
defense mechanism: in psychoanalytic theory, a defense mechanism whereby people attempt to hide their true motivations and emotions by providing reasonable or self-justifying explanations for irrational or unacceptable behavior
I find that the highlighted portion of what you said is the rationalization many use, not a true reason. I OC in Costco at least a few times a week in Bellingham and never have a problem. I OC in Banks, grocery shopping and don't seem to cause panic or nervousness.
Now there are the rare hoplophobic person who gets nervous around someone carrying a gun. But there are also homophobes who get nervous when a gay person is in the store, there are also xenophobes who get nervous when someone who doesn't share the same ethnic background share the same shopping space, there are women who are afraid of men..elderly afraid of teenagers, people who don't like bikers, punk rockers, gothers, etc. would they be asked to leave?
These are arguments we can use to defend the natural fundamental right to be armed. Something I have successfully used to destroy some unreasonable rationalizations like the one you pointed out.
By the way I have carried in Bellingham Costco countless times I go there at least twice a week. Our Costco has become so crazy, they pretty much have posted a full time cop right outside the doors. And I OC right past him/her often with a smile and a nod or wave.