I'm not sure I'd agree that people in groups 1 and 2 aren't worth engaging with.

The interesting bit to do for both cases is look at the 'they talk like a human' and 'are obviously somehow special' parts, separate the ideas of language, intelligence (memory, fluidity, abstract reasoning), _aliveness_ (as a biological process) and finally ideas about metacognition and theory of mind, and see whether their idea of consciousness as a super-bundle of the above (which is how I assume a lot of default ideas about consciousness are) actually sticks, or whether it falls apart when beings can have a subset of those properties but not all.

Also, I nominate myself to be in the 'People who have thought about it and are becoming more doubtful that I myself am conscious, and the question might be moot.' group.