Eventually there will be a mass shooting in one of these places and they’ll get sued for failure to enforce their ‘gun free’ policy. A false sense of security is no substitute for the real thing.
I think you're right. If by chance I was in one of these places or a family member was and anything happened with a firearm - including "just" a single shooting, brandishing, robbery, etc... I would hire the slickest shyster lawyer I could find and go after them for negligence and failure to ensure my safety even though they required me to disarm. Not just for any physical or emotional trauma, I'd go big on the "punitive" damages, like deep into 8 figures...tell the lawyer I'll cut him/her in for 50% to motivate them...