Actually, it's not.
When open carry was being promoted last year, a dumbass group of supporters took it upon themselves to demonstrate in Fort Worth fast food locations. They carried AR-15s into the stores and held them in a "ready" position with their fingers on the trigger.
They came off like a bunch of threatening thugs, ready to spray the customers on a moment's notice.
I can assure you that no restaurant chain wants that kind of behavior in their stores.
That particular incident also came close to sidetracking the whole open carry movement, as well.
Some ideas are so bad you have to suspect the organizer was working for the opposition.