Is it wrong to have sex with your brother or sister, even if no one is harmed?
Imagine for a second that a brother and sister are on vacation. They are alone, and there is no chance that they will be seen by anyone else. They both engage, consensually, in kissing, which leads to sexual intercourse. The brother and sister used protection, so there is no risk of pregnancy or disease. Both agree that it was an enjoyable experience, but that they wouldn't want to do it again.
If you are like most people, you find intercourse between a brother and sister immoral, and repulsive. In fact, work by University of Virginia professor Jonathan Haidt found that as many as 65% of people think that a brother and sister should be stopped or punished merely for kissing each other on the mouth in a secret hiding place.
Perhaps even more interesting, 45% of people thought that a brother and a sister enjoying kissing in private was always wrong, regardless of if a certain culture approves of it or not!
The majority of people also reported that it would be wrong to eat their dog (if it had already died) and to have sex with an uncooked (store bought, but dead) chicken.
Clearly, none of these perceived moral offenses harm anyone. So why are they so morally offensive to most people?
Haidt has found in his research that even when people can think of no good reason why something is immoral, they still often state that it is immoral. He dubs this "moral dumbfounding." People say things like, "I don't know why. It's just wrong."
So what does cause moral judgments? Haidt has compiled an impressive body of evidence indicating that our moral judgments are very influenced by our visceral, intuitive, emotional reactions and not as influenced by rational, conscious thought as most people think.
For instance, one study found that people who were hypnotized to experience disgust at certain words, later rated a person in the story containing those words as more immoral than people who were hypnotized, but not to feel disgust. In other words, people's moral judgments of the person in the story were caused by their unconscious associations between the words in the story and disgust (and not what the person did, which was the same in all conditions).
From this model of Haidt's, people's emotions decide, in a sense, what is moral or immoral for people. And then, the conscious brain kicks in, making post-hoc (after the fact) rationalizations and justifications for why people judge something as moral or immoral. This post-hoc rationalization process leads people to think their moral judgments are based on sound, rational thinking. But the truth is that people's judgments are made primarily (or at least a lot) by their intuitions and emotions.
This of course does not speak to the morality of any given behavior, but it does suggest that our moral jugments may be more based on gut level emotion than many of us tend to believe.