Welcome to the forum,
- First, I'll note that the manager was not correct, it is perfectly legal... however... private property is exactly that, and who own it is of no consequence. So in other words, there is no legal difference between a mom and pop, and a cooperation or large establishment. By refusing to leave when asked, you could face criminal trespassing charges (nothing to do with having the firearm). regardless of it being a firearm, or a t-shirt with Micky mouse, if the establishment doesn't want it there, then they have constitutional rights much like you and I. To be in line with supporting constitutional strength, we should respect and support those rights. The right way to fight it and make a change is to empower people around you to write and support the position we stand on, and encourage changes in their policy. Unfortunately the officer was not exactly correct either, they can prevent anyone from entering for any reason short of color race creed or sexual orientation. clothing, firearms and snack food, or just because they dont like one of us is fair game.
Read up through the WA forum section, there are some great peeps there with some excellent info. It's good to know your in the right before standing your ground.. it suck to find out the hard way if your wrong.
Take care, and welcome again.