How do you measure the intensity of desires, if not by introspectively comparing them (see below)? If you do measure something objectively, on what grounds do you justify its ethical relevance? I mean, we could measure all kinds of things, such as the amount of neurotransmitters released or activity of involved brain regions and so on, but just because there are parameters that turn out to be comparable for both pleasure and pain doesn't meant that they automatically constitute whatever we care about.
If you instead take an approach analogous to revealed preferences (what introspective comparison of hedonic valence seems to come down to), you have to look at decision-situations where people make conscious welfare-tradeoffs. And merely being able to visualize pleasure doesn't necessarily provoke the same reaction in all beings -- it depends on contingencies of brain-wiring. We can imagine beings that are only very slightly moved by the prospect of intense, long pleasures and that wouldn't undergo small amounts of suffering to get there.
How do you measure the intensity of desires, if not by introspectively comparing them (see below)?
You need intensity of desire to compare pains and pleasures, but also to compare pains of different intensities. So if introspection raises a problem for one type of comparison, it should raise a problem for the other type, too. Yet you think we can make comparisons within pains. So whatever reasons you have for thinking that introspection is reliable in making such comparisons, these should also be reasons for thinking that introspection is reliable for making comparisons between pains and pleasures.
I've always been more of a theoretician, but it's important to try one's hand at practical problems from time to time. In that vein, I've decided to try three simultaneous experiments on major Less Wrong themes. I will aim to acquire something to protect, I will practice training a seed intelligence, and I will become more familiar with many consequences of evolutionary psychology.
In the spirit of efficiency I'll combine all these experiments into one:
She's never seen Star Wars or Doctor Who.
She's never seen David Attenborough or read J. L. Borges.
She's never had a philosophical debate.
She's never been skiing.
Never had sex, never been hugged or even been licked by a dog!
She has so much to look forwards to...
(Though she'll be very boring for several months yet!)