There are medical reasons why some people cannot vaccinate, like the example of the boy who had a reaction. We had a wonderful little boy in ds's pre-school who was being treated for a rare form of cancer and could not have the normal vaccines. As such, it was extremely important that his parents and physicians knew that he was in school with fully vaccinated children.
I would want to know if my child shared a classroom with a child who was not vaccinated--if he were very sick, I would know to mention it to his pediatrician. Yes, vaccines protect the vast majority of those who have them but there are cases where someone could still get sick.
I also completely agree with pediatricians' practices who will not treat families where the parents decide not to vaccinate. It puts everyone in their practice at risk --especially any medically fragile children or infants who have to share the same waiting rooms and facilities.