You are right (of course, dang-it!) that there are differences between private property being used for a business and private property that I own for my personal use and enjoyment.
Either Florida or Texas, I can not remember which one, passed a law recently that said employees can leave a handgun in their cars while working. (Very rough interpretation of the law.)
The point I am trying to make is: What if the government made every company hire a mime? What if every company had to allow a mime to do what they do on your business property? What if every company had to give mime breaks?
(Thanks, now I can not get Marcel Marceau out of my head.)
Therefore, I still think the only real fix to the problem is tort reform. Take away the sword of liability hanging over the business owner's head, and much of the motivation for firearms bans will go out the window.
I agree 100%, but until that happens, I think the best response is still the letter writing.