Over the past year or so I've listened to some fantastic podcasts on ethics and read a book and Eliezer Yudkowsky posts on the subject. I have a hard time classifying what position I take on ethics, which is most likely motivated by the fond hope that one day someone will seek out my expertise and then sit rapt as I explain why I'm torn between the realist and anti-realist positions.
Beyond the Golden Rule, utilitarianism is the moral theory that most people are likely to have though about in some detail. It's intuitively appealing but also easy to think of utilitarian recommendations that most people reject. Utilitarianism is also assumed in just about all public discourse, though people seldom say so explicitly (we usually deny it).
I'm less phased by the horrible examples people use to discredit the theory than most people and have long thought of myself as a kind of utilitarian but I finally came accross a though experiment that really does make me pause.
There are about 10^(80) subatomic particles in the visible universe. So 10^(80) is a big number. 10^(90) is ten billion times bigger. Now imagine a number of the form 10^(999999999999999999999....) where you write the 9s as small as you can, and you convert all the matter in the universe into paper to keep writing 9s. The number you end up with is pretty big.
Now suppose there are that many people in the multiverse and you have to choose between all of them getting a speck of dust in their eye and one person being tortured for 50 years, what do you choose?
I choose the people getting dust specs in their eyes. This is difficult to square with utilitarianism, which makes me feel a bit weird.