There are good reasons on both sides of the discussion.
First: medical privacy is pretty well established as a right in the western world. Its pervasiveness thus, suggests a natural extension into missions in space.
But then: space exploration is still very, very experimental. In a deep sense, we do not understand the effects of space on human health. Yes, we know more than we used to, but we really know precious little. Any information about illnesses in evidence during or after space flight have critical importance for the future.
It's not unlike clinical trials, in that sense. No matter what adverse event happens when someone is in a clinical trial, it gets reported. When decisions are later made about approving the treatment under trial, the panel evaluates which events are relevant and which are not based on the evidence. The only difference is that with clinical trials, the data are anonymized, and there's very little chance of identifying which individual had which adverse event. But with spaceflight, there are so very few people involved, and their names are all public, so that process of identification would be / is reasonably straightforward. It might be that medical privacy cannot exist in practical terms, even though it should.
Having thought about it for the few minutes it took to reason through this missive, I'm of the opinion that we are still early enough in the development of spaceflight that medical privacy needs to be waived as a condition of being sent up. The greater good outweighs the individual's right to privacy in this case.