I feel that 2A was written to give people a means of defense and political power. Businesses should have no rights to regulate 2A in public areas.
Now, though, what about roller coasters? I might want to refuse to let guns on. Not everyone has a gun that is in drop-safe configuration, or has a holster with good enough retention.
Or what if I’m treating patients with different degrees of anesthesia? What if I’m giving therapy for schizophrenics?
For private areas, where no one else can effectively stand guard, I might not want untrusted persons to have their gun.