Some people have suggested (usually to avoid the conclusion of intelligent design arguments) that our universe is just one universe among many, and in fact there's a universe for every possible way things could have gone. Whole TV shows have been based on this claim. Tyler Cowen at Marginal Revolution discusses the ethical implications of the many-worlds thesis [hat tip: Philosophers' Carnival XXVIII] .
He argues that ethical questions would be irrelevant if this view is correct. No matter what you do, someone else just like you is doing each alternative possibility among the choices that were available to you. So if you can do the good thing or the bad thing, it doesn't matter which you pick, because your picking the bad one ensures that the good one will be done, and your picking the good one ensures that the bad one will be done. Either way the resulting multiverse is no different. Your action is simply irrelevant to what the multiverse will be like after your done. So ethics would be irrelevant. I disagree. This view doesn't have that consequence, and Tyler is just assuming something that I wouldn't grant.