We have many prima facie goals. But what they all have in common is that we will be pleased to achieve them. The things we want are the things that will make us happy. So, it seems that it's really happiness that is our ultimate goal, and our more particular ends are merely instrumental or implementations of this more general end.
The argument can be clarified further if restated in terms of desire: we want our desires to be satisfied, therefore what really matters to us to to achieve desire-satisfactions, and the particular things we now want are merely instrumental to the ultimate end of satisfying our desires in general. N.B. This implies that I could make you better off by inducing in you a strong desire to count blades of grass (and granting you access to a lawn).
The fallacy here derives from a kind of scopal ambiguity. It's true that we want our desires to be satisfied. That's tautological: we want to get what we want. But that latter 'what we want' should be understood de re rather than de dicto. We want to get those particular objects that we want. We do not merely want to have any old satisfied wants (e.g. induced desires that don't relate to our existing goals or values at all). Put formally:
(*) [Those X: WANT(i,X)] WANT(i,X)
"Of those things that I [now] want, I want them."
(#) WANT(i,[Those X: WANT(i,X)] X)
"I want that I get whatever things I [then] want."
Once we observe this distinction, hedonism and (#)-type desire satisfactionism lose much of their appeal. Why think that what matters most is happiness or desire-satisfactions in general? It's not what we actually care about, after all. (I'd rather struggle to achieve some of my philosophical and personal goals than be a satisfied grass-blade counter.) Why should our counterfactual concerns outweigh our actual ones?
(I could understand it if they were objectively more meritorious, perhaps, but the idea here is that their mere strength suffices to make them more important than our actual concerns. Satisfying particular preferences takes a back seat to promoting preference-satisfaction in general, including by means of inducing new preferences. Compare G.A Cohen's objection to utilitarianism, which is a more radical version of my complaint here, since he applies it even to objective values, and not just subjective ones.)