Doesn’t this analogy backfire? Science corrected miasma theory because it has a method for testing claims against reality. Morality has no such method, which is why some conclude moral claims can’t be true or false at all.

The analogy is meant to make one narrow point: that widespread agreement can be wrong, and that true means matches reality, not currently believed. It does not show that morality has a reality to match; that argument is made separately under the claim about a moral source beyond human beings. The disanalogy is also smaller than it first looks. Moral reasoning does have methods (consistency, testing principles against cases, reflective equilibrium), even if they are not laboratory methods, and people use them to change their minds about slavery, torture, and the treatment of children.