Natural right to medical treatment?

From a response to my friend, The Real Pianist:

The concept of natural rights is currently misused by the Left. “Natural right” is a tool of the natural law to assign property claims in order to resolve conflicts. One can have a right to something he owns. One cannot have a right to something he does not own, to be provided by others to him for free, since it contradicts the concept of their natural right to their property.

This confusion comes from the mixing of the concepts of natural rights and contractual rights. Under normal circumstances, Bob does not owe anything to Joe. If Joe gets sick, he does not have a right to Bob’s property, since, as I mentioned above, it contradicts Bob’s right to it. But, if Bob is a doctor, and Joe paid Bob for treating him, then Bob does owe Joe some services. This is because a contract has been made between them. Bob's treatment of Joe is the latter's contractual right.

So, the only situation when someone might owe something to someone else is if he has contractually obligated himself to provide this specific thing.

Modern Liberals mix the two concepts. One has a natural right to life in the sense that one has a natural right to his body and therefore has a right not to have life taken away from him by aggression. That is what a natural right is. But Liberals treat the natural right to life as if it were a contractual right that is owed to an individual by the society. Therefore, if an individual gets sick, the society owes it to him to pay for his treatment. But one can never have a natural right to others' property. One can only have a contractual right to their property if they — the specific members of the society — have contractually obligated themselves to provide the specific service.