Full Idea
The pleasantness of pleasure is not in dispute, but where we say the majority of pleasures are bad, though some are good, you are attributing goodness to all of them.
Gist of Idea
Pleasure is certainly very pleasant, but it doesn't follow that all pleasures are good
Source
Plato (Philebus [c.354 BCE], 13b)
Book Reference
Plato: 'Philebus', ed/tr. Waterfield,Robin [Penguin 1982], p.54
A Reaction
Bentham's plausible view is that the feeling of pleasure is always good, and the badness is in some other aspect of the event. Compare sadistic fantasy with sadistic action.