Any hospital that posts a prohibition on firearms has the law on its side.
I think he phrased it badly. It would be more accurate to say that until they tell you to leave no crime is committed by carrying in most hospitals. Even if they do tell you to leave, no crime is committed unless you refuse to. Of course, if you're a patient and physically cannot leave or would risk death if you did, the law is a lot less clear.
In places where carry is actually prohibited by law, carrying is worth an arrest and charges as soon as they see you doing it.
What happens when exercising your right, in violation of a property owner / operators wishes, actually causes a reaction that actually hurts other people by disrupting care? What is the moral decision?
Is the hospital guaranteeing that their patients, clients or family of same will not need to defend themselves on the premises, in the parking lot or during the drive to or from the hospital?
If you comply with hospital policy and render yourself helpless, is the hospital liable if you are attacked while seeking medical care, in a situation where defending yourself effectively would have saved you?
If a crazy person freaks out and acts irrationally, does it create a crime or attack where none actually exists, or is that person merely crazy?