David Sosa does a nice job of explaining at least one reason why happiness is not pleasure (involving Nozick's experience machine, etc.). But what exactly is the difference between merely feeling that you are having desirable experiences and actually having them? The unreal experience is not really bad. It's just not very significant, as Sosa points out. Happiness, he seems to think, has a significance that comes from reality. So dreams and drug-induced feelings might be pleasant, but they don't make someone happy. And that sounds about right.
It would be nice to be able to give an account, though, of why this is so. What exactly is significance? What exactly is its connection with reality? And how much, or what kind of, difference does it make if we manipulate reality to make it provide the kind of experiences we want to have?
Examples might help make clearer what I have in mind. The pleasure of winning a race seems real, and better (not necessarily more pleasurable) than the pleasure of 'winning' a virtual race on a computer. The same would go for winning fairly rather than winning by bribing a referee to disqualify a rival. But what about winning because of steroid (ab)use? Shooting fish in a barrel has go to be less of an accomplishment than catching a fish the normal way, even if the shooter is unconcerned and gets great pleasure from shooting fish. A friendship with a real person seems much more valuable than a 'friendship' with a robot companion that has been trained to be friendly.
But a) is what seems to be better really better in all these cases, b) how can we know (Mill's test of asking those who appreciate both pleasures?), c) why is the better one better? I don't think the answer to that is only that the inferior pleasure is gained immorally or by cheating. Reality is at stake as well as ethics.
Somehow it seems to me that reality itself has a kind of value, and this relates to what I was trying to get at here. It also relates (if only in my imagination) to something wrong with McMahan's expressed desire to radically re-design reality.
Slightly relevant but ridiculous video: