The argument is about the evidence for red wine’s cardiac benefits, not whether physicians should advocate its consumption.

The health benefits of red wine are supported by statistical evidence. The issue, according to the author, is that supporters of red wine cannot explain what precise mechanism creates this result.

The argument isn’t about when physicians should make recommendations — it’s about whether the existing evidence is conclusive. It could simultaneously be true that physicians should sometimes make recommendations without conclusive evidence, and that the existing evidence is not conclusive.

This principle is necessary to underpin the stimulus. If it is not required to know the specific mechanism for evidence to be conclusive, then the evidence linking red wine to cardiac benefits would be conclusive and the argument would be invalid.

The argument makes no conclusion about under what circumstances one should try to find a causal mechanism — it only argues that without knowing that causal mechanism, evidence cannot be considered conclusive.