Here's a link to the justifications participants offered in the moral dumbfounding study Paulo Sousa and I conducted - "Study 3" in our SPPS paper:
Piazza, J., & Sousa, P. (2014). Religiosity, political orientation, and consequentialist moral thinking. Social Psychological and Personality Science. (See publications for full reference).
Here's a summary of what we found:
--There were primarily three categories of justifications participants offered for their impermissibility judgments (i.e., those who persisted to say that the act was "wrong"; 46% consensual cannibalism; 56% consensual incest):
(1) deontological statements (i.e., appeals to an existing normative proscription within the subject's culture) or restatements of the wrongfulness of the act
(2) appeals to emotion (e.g., disgust)
(3) appeals to hidden, psychological, or long-term negative consequences of the act
--Deontological statements were by far the most common response.