As a general principle, I believe that private property owners should be able to declare their properties to be “gun free zones.” I can think of several kinds of businesses that might want to keep firearms away. For example, the muzzle flash from a firearm could cause a serious disaster in an industrial plant with volatile fumes in the air. Also, some people are hoplophobes and have an irrational fear of weapons; they should be entitled to their “safe spaces.” However, they should have to accept the consequences for doing so.
IANAL, but it seems to me that something analogous to the attractive nuisance doctrine should apply to such properties. Just as person who has an unfenced swimming pool can be held liable for a someone wandering into the pool and drowning, a property owner who invites visitors (especially, customers) into a “gun free zone” should be held liable (perhaps strictly liable) for the visitors’ safety.
Rights have responsibilities attached.