And how do YOU arrive at the conclusion that pleasure is the highest good?
Well, I haven't been thinking about it in terms of the highest good, but that's a good idea.
Off the top of my head, I'd say pleasure is the highest good because for any other good, you can always ask why is it good, and you should get an answer. When you get to "because it gives me pleasure", that's the end of the line.
Hmm...maybe that's all that's necessary?