I don't see how this answers my objection. I'll try to restate my main point in a more clear form.

The claim that "'healthy' is not a precisely defined concept, but no one is crazy enough to utter that medicine cannot answer questions of health" is, while superficially plausible, in fact false under the interpretation relevant for this discussion. Namely, the claim is true only for those issues where the concept of "health" is precise and uncontroversial. In situations where the concept of "health" is imprecise and a matter of dispute, there are sane and knowledgeable people who plausibly dispute that medicine can legitimately answer questions of health in those particular situations. Thus, what superficially looks like a lucid analogy is in fact a rhetorical sleight of hand.

(Also, I'd say that by any reasonable measure, questions of health vs. disease are typically much more clear-cut than moral questions. The appearance of coughing or headaches, ceteris paribus, represents an unambiguous reduction of health; on the other hand, even killing requires significant qualifications to be universally recognized as evil. But my main objection stands regardless of whether you agree with this.)