Because I wouldn't know what it would mean for a situation to be good or desirable except in relation to pleasure/pain. It seems to be a contradiction in terms.

And you, then, assume that since you wouldn't know, no one could possibly do.

Moreover, you insist that everyone who thinks in more complex terms than just pleasure and pain is mistaken in their beliefs and really wants just pleasure and nothing but pleasure.

Correct?

Because I wouldn't know what it would mean for a situation to be good or desirable except in relation to pleasure/pain. It seems to be a contradiction in terms.

I don't believe you. I believe that if caught unawares (without the time to rationalise) you will rapidly and intuitively make value judgements about things and convey them both via word and deed. For example you will not act as if you are perfectly OK for billions of (relative) innocents to be slaughtered so long as you are wired to feel pleasure regardless of that occurrence. You may be able to verbally declare that kind of value if the situation is contrived enough for you to be thrown into 'far-mode' (abstract philosophical thinking) and can reframe everything into idealised hedonistic terms but if the scenario were more subtle and presented in a non-philosophical context you would act more like an actual human being.

No insult intended. My skepticism means "I don't believe you are as insane as you claim you are."