Empiricism and the scientific method are a philosophy for modelling reality, and they've undoubtedly done a bang up job of progressing human understanding, but that model is also incomplete. Think of it like Newtonian gravitation, another undoubtedly very useful model that, it turns out, is also incomplete.
So I don't agree that consciousness in general can't be tested for. We can test our own consciousness, and we can use induction to guess that at least other humans are experiencing something similar.
A minor, but important point. I don't assume it's true. I just think it is more likely than not.
I suppose that the philosopher I'm talking about could say the same of their theory. And I guess that's OK, if all they're claiming is that this is something that seems likely. My only response to that would be that his induction is prima facie questionable to me.
The theory can’t be tested by experiment, but I do think it can be critiqued in terms of internal logical consistency. In that regard, a well structured theory of consciousness could have powerful structure, and much like abstract mathematics lead to practical results.
This is a very materialistic view of the world. By this measure we shouldn’t talk about religious ideas or discuss the (non-monetary) value of art. I have great respect for science, but I think there are things worth discussing that fall outside of science.
It's hard to exactly word my objection. I feel like people view philosophers as being in pursuit of the truth -- trying to understand and reason about how reality is. They have this reputation in a way that's entirely different from the reputation of artists, who folks generally recognize as producing work that is not claiming any kind of authority about reality. At one point in time, that may have even been the case. But I think, at least for philosophers who promulgate ideas like this one, the level of authority should be similar to that of an artist, or maybe a poet. The philosopher is not talking about reality, he's just putting some words together in a way that is interesting to some people.
(Your view of religion, IMO, both shortchanges it and gives it too much credit. I suspect most religious adherents would at least claim to believe that their religion does make predictions about reality that are or at least will be testable. Perhaps you won't be able to conduct that test while living, or at the present time. But at least most sects of Islam and Christianity expect that the god of their religion will at some point impinge on our material reality, and has done in the past. I am less familiar with Shinto, Buddhism, and Hinduism, but I'd be surprised to hear that most adherents of these religions view their religion's claims as generically and permanently untestable.)
I generally agree with you though -- we'd be better off if we just focused more on science, and describing things accurately, instead of just coming up with wild ass ideas. But it still is good to acknowledge and be aware of known limitations with that approach.
For example, the interpretation of natural numbers as sets in set theory and as strings of decimal digits is equivalent and gives the same results, however for most people seeing numbers as naturally being strings of decimal digits is likely to make them faster at doing arithmetic and making decisions based on numbers.
Likewise, seeing other people as conscious or unconscious results in the same predictions about their behavior, but seeing them as conscious might make most people more efficient at cooperation with other people.
In this case, seeing all matter as conscious might make someone feel less special, and thus have less attachment to their identity and spend less effort acting in a way that preserves it.
But this philosopher's claim isn't subjective. It's not "hey I think it would be cool if all matter were conscious." It's a pseudo-factual claim about consciousness. It's not subjective at all. It's just neither wrong nor right. It would be like me claiming that there exists a being called "god" who has never and will never interact with this universe in any way. You can't predict anything based on this pseudo-factual claim, which means (IMO) it has no real truth value. On the other hand, it's definitely not a "subjective" viewpoint as most people conceive of subjectivity.
For example, playing a video game, there is some kind of objective physical activity occurring in reality. Subjectively, you perceive a cartoon world with Mario bouncing around on koopas. If the CPU has its own subjective experience of the very same objective physical phenomena, it probably doesn't involve the perception of Mario and koopas.
I think there is probably tremendous value in figuring out what it is about the universe that enables these different subjective experiences, when and how they arise, how they're similar and different, etc.
But in turn I can say everything you know and experience about the world is subjective. It came through your senses and you have no way to know if it was the same with other people.
Mathematics is also "untestable" in the same way. You can't observe that the world would behave differently whether or not 2=2 or 1=2. Does this make mathematics practically useless, except as a form of entertainment?
Furthermore, why is entertainment spoken of as a lower purpose than "practical uses"? I very much doubt you'd want to live in a world without such "entertainment".
I would almost argue that it doesn't make sense to talk about something being true or untrue if it cannot be tested nor used to make any predictions. The whole concept of truth, for me, reflects the extent to which reality conforms to belief. So if there isn't and will never be a way to test a belief, then it's neither true nor false.
IMO, this is the type of thinking that gives philosophers a bad rap.