Maybe neuro science will prove it someday.
Can there be anything "good" without a positiv affection ? Isn´t that ( positive affection / pleasure ) and the desire for that, what differentiates us against robots ?
When Pleasure/Pain is the core of all personal values than it is the only intrinsic good. But yes we must separate Pleasure and the consequences that have to be evaluated separately against further Pleasure/Pain.
The Stoic say that Virtue leads always to good things, Pleasure not. For that the separation is crucial. With this analysis I can see, that the statement "Virtue is always good, Pleasure not " has this problems:
1. That it is just a defintion (tautalogy) ( Virtue (the good) leads to good things/outcomes )
2. Good things / outcomes are externals for Stoics so cannot be good (in their own definition) so Virtue leads only to no-goods (indifferents/externals)
3. When Virtue is good because it always leads to good outcomes, than there is a differentiation between Virtue and "Good", so 2 separate things and Virtue gets good because of the outcomes (= what makes Virtue instrumentally and valuable only because of the outcomes)
4. And how do we value "good things/outcomes" ? With affection, feelings, so we judge everything with our feelings, in the core with Pleasure / Pain and also we judge their consequences with Pleasure/Pain.
Thats currently my prove that Pleasure is the supreme intrinsic good and not Virtue which is the greates instrumental good with its core phronesis (prudence ) and philia (friendship) which both are the basics for every ethic / moral. In my Opinion