Figure out how many victims you would dustspeck in exchange for two beneficiaries having a high-quality sexual encounter
I guess you meant "how many sexual encounters would you demand to make a million dustspecks worthwhile". And my emotional response is the same as in the original dilemma: I find it reeeallly icky to trade off other people's pain for other people's pleasure (not a pure negative utilitarian but pretty close), even though I'm willing to suffer pain myself in exchange for relatively small amounts of pleasure. And it gets even harder to trade if the people receiving the pain are unrelated to the people receiving the pleasure. (What if some inhabitants of the multiverse are marked from birth as "lower class", so they always receive the pain whenever someone agrees to such dilemmas?) I'm pretty sure this is a relevant fact about my preferences, not something that must be erased by utilitarianism.
And even in the original torture vs dustspecks dilemma the answer isn't completely obvious to me. The sharpest form of the dilemma is this: your loved one is going to be copied a huge number of times, would you prefer one copy to be tortured for 50 years, or all of them to get a dustspeck in the eye?
I find it reeeallly icky to trade off other people's pain for other people's pleasure
Does it work the same in reverse? How many high-quality sexual encounters would you be willing to interrupt while you are out saving people from dustspecks?
Most of the usual thought experiments that justify expected utilitarialism trade off fun for fun, or suffering for suffering. Here's a situation which mixes the two. You are offered to press a button that will select a random person (not you) and torture them for a month. In return the machine will make N people who are not suffering right now have X fun each. The fun will be of the positive variety, not saving any creatures from pain.
1) How large would X and N have to be for you to accept the offer?
2) If you say X or N must be very large, does this prove that you measure torture and fun using in effect different scales, and therefore are a deontologist rather than a utilitarian?