Robin was clear about what he meant by "opinion". From his first paragraph, with emphasis added:

You are entitled to your desires, and sometimes to your choices. You might own a choice, and if you can choose your preferences, you may have the right to do so. But your beliefs are not about you; beliefs are about the world. Your beliefs should be your best available estimate of the way things are; anything else is a lie.

Though I agree that it can cause problems to use "opinion" in an unusual way, even in the context of explicitly stating one's unusual definition, when people are going to quote the conclusion as a slogan out of the clarifying context.

On the other hand, "You are entitled to your utility function but not your epistemology" would not make an effective slogan. (Well maybe, if it has enough "secret knowledge" appeal to motivate people to figure out what it means.)