What is the name of this fallacy? I can't seem to find any reference to it on the 'net. It may seem too simple to be a common fallacy, but I don't find that to be the case.
For instance, Hume (it can be argued) says that the only things that are right are things we prefer. A possible objection to this might be, "So then you're claiming that everything someone wants or prefers is right?" An answer to that, of course, is that just because everything that is right is something we prefer, that does not imply that everything we prefer is right.
I'm not interested in getting into a discussion on Hume; I'm just trying to lay out a case where this fallacy might come into play.