To give a concrete example of where the dividing line is. Take health care. Certain forms of health care are certainly public goods. Others most certainly are not. One that definitely is is the herd immunity provided by a good vaccination campaign. Take, oooh, say, measles. For most people who get this disease it’s a pain for a week or so of childhood. For some small portion of those who catch it it leads to blindness, brain damage, even death. Clearly, a vaccination against measles is not a public good. The vial of vaccine used upon me cannot be used upon you. We can also with hold vaccines from people we don’t like (this is not a serious comment but it does show that a vaccine is excludable). However, imagine that we vaccinate 90, 95% of the population? There is now no chance of an epidemic spreading. Indeed, there’s not really anywhere in the population for the disease to exist. Thus even those who have not had the (rivalrous and excludable) vaccine are protected from the disease as well. That’s the herd immunity: and that is indeed non-rivalrous and non-excludable.