I don’t think they do need to defend that claim - since it’s not a claim any of them make in the first place. When ethical subjectivists analogize moral judgments to gastronomic judgments, they’re analogizing them in a specific respect: for example, that they’re both alike in that the truth-makers of both judgments are something subjective rather than objective.

The fact that both judgments are alike in this respect doesn’t mean they’re alike in other aspects too. When a moral realist compares moral judgments to logical judgments, one could respond by pointing out that logical judgments aren’t normative whereas moral judgments are. This is a disanalogy between the two, but it’s not a relevant one, since the point of comparison is that both judgments are made true by something other than our stances.

Or when a non-naturalist compares moral judgments to scientific judgments, one could point out that the non-naturalist comes to scientific judgments via empirical inquiry, whereas they don’t do the same for moral judgments. Again, a disanalogy, but not a relevant one.

Likewise, when an ethical subjectivist compares moral judgments to gastronomic judgments, one could respond by saying that the subjectivist doesn’t condemn people for having differing gastronomic judgments but does when others hold differing moral judgments.

That’s true, but that doesn’t mean the subjectivist is wrong in comparing the two with respect to their meta-normative status. That gastronomic and moral judgments are alike when it comes to both being subjectively true is compatible with them very different in other respects.