Occasionally several different ideas come together in an interesting way. The following came up in conversation today, and tied several ideas together in what was for me an enlightening way.

First the uncanny valley. This is the hypothesis that things which seem to us to be almost, but not quite, human elicit a very strong negative response. We do not experience this response to things that are very much not human, nor to things that are clearly human. You can read http://en.wikipedia.org/wiki/Uncanny_valley for more on that effect. If you can get http://www.cubo.cc/creepygirl/ to render for you, you'll probably experience the effect for yourself. (The link is sometimes down.)

Next cognitive dissonance. When people become aware of a contradiction between two things that they are experiencing, they get a feeling of discomfort, and you will naturally attempt to resolve that discomfort. Resolutions commonly include rejection, and often can involve strong emotional reactions. It is doubtful that cognitive dissonance by itself is an explanation of the uncanny valley, but it certainly doesn't help any.

One source of cognitive dissonance is categorizing things that don't fall into your neat categories. For instance The Structure of Scientific Revolutions described one classic experiment with cards, some of which were "impossible" - such as a black queen of hearts. People who had not yet figured out what was going on couldn't see that card for what it was and often reported physical discomfort from it.

Next, attribution error. If I am feeling X when I interact with Y, I will tend to associate X with Y, even when they clearly have nothing to do with each other. Sounds obvious? It isn't really. See http://youarenotsosmart.com/2011/07/07/misattribution-of-arousal/ for examples of some of the surprising results experiments have demonstrated that come from that effect.

And finally biases that people have around gender and sexual identity. As odd as it seems today, 150 years ago women wearing men's clothing were lynched. 50 years ago in most of the USA it was illegal for couples of different races to marry. Blatant homophobia is common. I've heard that most trans people at least once will get beaten up after revealing that that they are trans to a love interest. And today the US public is fairly evenly divided on whether gays should be allowed to marry - even many people who claim not to be homophobic get creeped out by the idea of gay marriage. Why do things involving other people, that clearly does you no direct harm, cause such strong emotion?

Here is the possible explanation that came up. Gender is for virtually all of us a basic attribute that we categorize people on. When people fail to easily fall into our gender category, we experience cognitive dissonance. That can cause us to be throw them into the uncanny valley, resulting in discomfort. It is easy for us to wrongly attribute that discomfort to the person, then take it out on them.

So in a culture where clothing equals gender, a person wearing clothing of the wrong gender can trigger that effect. In a culture where marriage is only between like people, a marriage between people of different race can trigger that effect. To a person for whom men and women are only supposed to be attracted to the opposite gender, someone who is attracted to their own can become revolting. The shock of realizing you were attracted to a "man" can be severe - and gets taken out on your former interest. And even someone who can accept that gays are attracted to each other may have a tremendous amount of trouble with the idea that they can fall in love and commit just like any other couple.

At an emotional level I still don't understand these negative reactions. I don't personally have those reactions. However I feel that I now have a better intellectual handle why some people have intense emotional reactions on these issues.
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