I believe it is also useful to analogize this question to Epicurus' analysis of the boundlessness of space. We can throw the javelin endlessly and never hit the end of space, and yet the universe has a logical limit in being composed of only matter and void, outside of which nothing exists or can be conceived to exist as possibly entering the universe from outside to change it.
Pleasure and pain stand in the role of matter and void - it is useful to consider them from the perspective of quantity for some purposes, but no one should be so foolish as to forget that the matter and space composing my body and my mind are much different to me, and of much more concern, than the matter and space composing a rock on the far side of the moon.
The rock and my mind may be equivalent in quantity (weight) but they are dramatically different in most other,and most important respects, about which"quantity" tells us nothing.
Why are we talking about these absurdities? Only because Plato and the logicians seek to avert us from pleasure by arguing that the greatest good in life must have a "limit."