This is a brief summary of materialist, or "physicalist", theories of mind.
The mind is just brain activity. Talk of mental events (pain) can be swapped out with talk of physical events (firing of C fibers) on a one-to-one basis.
The success of science in explaining everything else in terms of matter/energy.
There could be other intelligent creatures, such as aliens or artificial intelligences, that have minds but a completely different brain structure. They could be able to feel pain but instead of C fibers they might have some other cells that fulfill the same role. This naturally leads to...
Mental events can be realized by many different types of physical systems. Pain could be C fiber firings in humans, and gamma firings in aliens. Talk of mental events cannot be swapped out with talk of physical events, since those physical events might be different in different species.
It is highly plausible that mental events can be realized by many different types of brains, as we see even with different animals here on Earth.
Can first-person subjective experience be accounted for or explained if the mind is nothing more than a program or functional algorithm?
There is no mind. There is only brain activity as described by neuroscience.
Talk of events like beliefs, desires, fears, and other mental events is like a folk theory, and it is fruitless. Therefore, this folk theory should be eliminated and we should say there are no such events as beliefs, desires, fears, etc.
Can we really accept that there are no beliefs, desires, fears, or other mental events? Is that at all plausible?