In my humble opinion, open carrying is just asking for undue attention from citizens, employees, and perhaps law enforcement (if they get called by citizens or employees). If you are willing to deal with that attention, then more power to you! I choose not to, but that is (of course) just my choice!
Fact is, guns scare many people in our society, and it doesn't fit with the "norms" of our culture these days!
We all know that... And we should all expect that this kind of things is going to happen if we do choose to open carry in a grocery store! Good or bad, it is reality.
Just because you have the right to do something, doesn't mean that doing it is something I would recommend. For example, you could be well within your legal rights to tattoo a swastica on your forehead, but it doesn't mean that you will be readily accepted in society! Likewise, if you stood in the middle of a Walmart store while exercising your 1st ammendment rights to tell everyone that you didn't support Walmart's "big business" tactics, they would probably be inclined to tell you to leave the property! Either of those examples are legal, and neither (on it's own) could get you arrested.
Also, around here stores have the right to ask someone to leave their property. If they tell you to, and you don't, it is trespassing. Obviously you could always file a complaint with their corporate office... But, if I show up at Walmart, and the staff tells me that they ask a person to leave, and that person refused, then it is my job to make them leave or arrest them. (not saying that this situation rose to that level... but just clarifying that a private business is often allowed to tell someone to leave).
So, if you like to open carry, more power to you. Just be prepared to get a bit of attention that you normally wouldn't, and be prepared to leave the property if you are told to by an employee or law enforcement officer (if the laws are the same in that part of the country).