And they have a negative reaction because they have cognitive dissonance with what is presented to them. They're forced to either reject the alternate moral judgement and be hostile to it (in some sense, not directly), or accept it and change their behavior.

Even subjective "preferences" such as "I like soft-drinks" have logical consequences, or implicit decisions associated with them. I.e. "I am fine with hurting my long-term health because I enjoy the immediate rush of soft-drinks." Not every can live their lives in a completely evidence-based, logically-optimized way.