That is a start, but we can't gather data from entities that cannot speak
If you have a mind that cannot communicate, figuring out what it feels is not your biggest problem. Saying anything about such a mind is a challenge. Although I'm confident much can be said, even if I can't explain the algorithm how exactly that would work.
On the other hand, if the mind is so primitive that it cannot form the thought "X feels a like Y", then does X actually feel like Y to it? And of course, the mind has to have feelings in the first place. Note, my previous answer (to ask the mind which feelings are similar) was only meant to work for human minds. I can vaguely understand what similarity of feelings is in a human mind, but I don't necessarily understand what it would mean for a different kind of mind.
and we don't know how to arrive at general rules that apply accross different classes of conscious entity.
Are there classes of conscious entity?
Morality or objective morality? They are different.
You cut off the word "objective" from my sentence yourself. Yes, I mean "objective morality". If "morality" means a set of rules, then it is perfectly well defined and clearly many of them exist (although I could nitpick). However if you're not talking about "objective morality", you can no longer be confident that those rules make any sense. You can't say that we need to talk about robot pain, just because maybe robot pain is mentioned in some moral system. The moral system might just be broken.
If you have a mind that cannot communicate, figuring out what it feels is not your biggest problem. Saying anything about such a mind is a challenge. Although I'm confident much can be said, even if I can't explain the algorithm how exactly that would work.
It seems you are no longer ruling out a science of other minds, Are you still insisting that robots don't feel pain?
but I don't necessarily understand what it would mean for a different kind of mind.
I've already told you what it would mean, but you have a self-imposed problem of tying meaning to ...
(This post grew out of an old conversation with Wei Dai.)
Imagine a person sitting in a room, communicating with the outside world through a terminal. Further imagine that the person knows some secret fact (e.g. that the Moon landings were a hoax), but is absolutely committed to never revealing their knowledge of it in any way.
Can you, by observing the input-output behavior of the system, distinguish it from a person who doesn't know the secret, or knows some other secret instead?
Clearly the only reasonable answer is "no, not in general".
Now imagine a person in the same situation, claiming to possess some mental skill that's hard for you to verify (e.g. visualizing four-dimensional objects in their mind's eye). Can you, by observing the input-output behavior, distinguish it from someone who is lying about having the skill, but has a good grasp of four-dimensional math otherwise?
Again, clearly, the only reasonable answer is "not in general".
Now imagine a sealed box that behaves exactly like a human, dutifully saying things like "I'm conscious", "I experience red" and so on. Moreover, you know from trustworthy sources that the box was built by scanning a human brain, and then optimizing the resulting program to use less CPU and memory (preserving the same input-output behavior). Would you be willing to trust that the box is in fact conscious, and has the same internal experiences as the human brain it was created from?
A philosopher believing in computationalism would emphatically say yes. But considering the examples above, I would say I'm not sure! Not at all!