Rigorously, I think the argument doesn't stand up in its ultimate form. But it's tiptoing in the direction of a very interesting point on how to deal with changing utility functions, especially in circumstances where the changes might be predictable.

The simple answer is "judge everything in your future by your current utility function", but that doesn't seem satisfactory. Nor is "judge everything that occures in your future by your utility function at the time", because of lobotomies, addicting wireheading, and so on. Some people have utility functions that they expect will change; and the degree of change allowable may vary from person to person and subject to subject (eg, people opposed to polygamy may have a wide range of reactions to the announcement "in fifty years time, you will approve of polygamy"). Some people trust their own CEV; I never would, but I might trust it one level removed.

It's a difficult subject, and my upvote was in thanks of bringing it up. Susequent posts on the subject I'll judge more harshly.