There is no evidence that their stated preferences are not their preferences.

That's an incredibly strong claim ("no evidence"). You are giving rather a lot of privilege to the hypothesis that the public relations module of the brain is given unfiltered access to potentially politically compromising information like that and then chooses to divulge it publicly. This is in rather stark contrast to what I have read and what I have experienced.

I'd like to live in a world where what you said is true. It would have saved me years of frustration.

You have to assume that how humans acts says more about their preferences than what they say about their preferences.

Both provide useful information, but not necessarily directly. fMRIs can be fun too, albeit just as tricky to map to the 'want' concept.