You are confusing physicalism and determinism. Just because physicalism is true, does not mean determinism is. You are assuming a particular kind of causality is necessary to a physicalist account of the universe, and it isn't.
My thesis is about morality, which is (I take it) the way persons ought to be or act. All persons, not just the ones we know exist. I do not believe that you cannot think of entities that have not been thought about by the "great philosophers" for a moment. But, taking this to mean instead that we shouldn't bother with entities that haven't been conceived of by the "great philosophers", I think you are just wrong. I don't know how we would go about solving philosophical problems or making philosophical progress if we didn't think of things that haven't already been conceived of (although I don't think this is actually an example of this as it seems that plenty of people have considered persons who do not experience pain or pleasure before).
I agree that causality is not necessary to complete a physicalist account of the universe,(but I would'nt bet much on my belief's being true it is in fact a pro tem belief) and I'd also say that determinism is not necessary for the universe to exist, mainly based upon an entirely new idea I just got from Sanchez, and which I have not sufficiently thought about
Daniel, you wrote:
I do not believe that you cannot think of entities that have not been thought about by the "great philosophers"
but that's not what I said. What I said was , not entities, but ontological entities. Perhaps I'd have made myself clearer if I'd said ontological substances, and substances would certainly be more correct than 'entities'. However I had hoped that 'ontological' would give the clue to what I meant.
Certainly I do believe that philosohers can be creative. However I cannot see what ontological choices, i.e.what theories of existence, could remain besides:-
1. Cartesian or substance dualism
2. monisms
a)idealism (immatterialism)
b) physicalism (materialism)
3. Dual aspect monism
If you know of any other please tell. In all sincerity I say that the above are all the theories of existence I have ever heard of. My reading is not entirely up to date I confess. However if there were a new theory of existence it would have been headline news, a paradigm to put all other paradigms in the shade.
I do endorse metaphysical speculations, and indeed thought experiments. This includes that physical life forms other than our familiar carbon based one should be speculated about, and for all I know be material for experiments. People who don't experience pain or pleasure are commonly thought of as deficient in qualities that are necessary for them to live independently of help from others, and if the help is not forthcoming such unfortunate people tend to die sooner and sometimes, where the judiciary is unenlightened, in prison.
Subjective sensations of and comprehension of pain and pleasure together with their physical correlates are adaptations to environment. I can provide examples of pathological anaesthesia.
Consequently any alien life form would need some facility for maintaining its integrity otherwise it would be unable to separate itself from its environment, would become one with its environment and so would not exist as entity.
Besides the plain natural description of pain and pleasure, above, perhaps Pain and Pleasure are Platonic Forms . If you would like to talk about the ethical implications in Platonic Forms that would be a very interesting discussion.