If it's too slow to interact with the rest of the world in appropriate ways, it wouldn't be a consciousness at all.
Of course, part of the difficulty of imagining a conscious rockputer is that it's also pretty hard to imagine its inputs :)
This is trivially true as you state it; that's why I added the qualifier "in appropriate ways". Not all interactions will produce consciousness. One obvious difference between us and your hypothetical "rockputer" is that the "rockputer" can't change its behavior based on its inputs in a way that improves its chances of survival; rocks simply aren't built that way. Neither are star systems or galaxies. But we are.
Yes it can. Some natural events, for example a flood or an earthquake, can destroy parts of the rockputer. It is therefore important for it to store the various parts of itself strategically. It shouldn't put its vital parts near the coast, or a tsunami may kill it. It should store its own consciousness in a robust way, so that it can recover from an earthquake. It's probably too slow to actually see either of them coming, but it can certainly prepare itself.
Or imagine you build two rockputers, one with black stones, another with white stones, and you have rules to remove stones when both rockputers try to expand into the same territory, a bit like in the game of Go. Then one can kill the other.
Star systems interact with each other through gravity, so you could conceive of them as some kind of gargantuan atoms, capable of making complex structures, including conscious ones. Granted, there doesn't seem to be an equivalent of the other forces at that scale, so probably it wouldn't work, but you see what I mean.
The level of complexity of the "passive" components of the system (i.e. the rocks) is irrelevant to whether or not the system can effect conscious-seeming behaviour when acting dynamically. Analogously, the underlying components of people, i.e. atoms, are clearly quite dumb on their own. When those atoms are allowed to evolve collectively over time, according to dynamics dictated by basic physical laws, conscious-seeming behaviour magically appears.
You can't deny the possibility of a conscious rockputer just by considering properties of the rocks.
Yes, and in that case, all the actual computation is being done by the mechanism, not the rocks. As you say, the rocks are just "passive" components.
I agree that, in principle, such a system could compute; but it still has the problem of computing on a time scale that supports appropriate interactions with its environment. Moving rocks around in accordance with some set of computational rules based on inputs is very slow--quite possibly too slow to respond appropriately to inputs. For example, if incoming light rays are carrying information about a tidal wave that is about to swamp the rockputer and destroy its structure, could the rockputer compute an appropriate response (such as moving itself to higher ground) quickly enough to save itself?
I don't think this is as absurd as it sounds. I think it was Dennett who said our intuition about consciousness is pretty sensitive to timing. The rock construction you describe would "think" a billion times slower than a human brain, and there is something unsettling or unintuitive about a consciousness that operates in slow motion. I would expect extremely fast-paced AI to think that the idea that human beings are conscious is similarly absurd.
Also, consciousness "feels" like it's ineffable, so it makes sense that we would have an inherent bias against understanding it as a process. There is something we see in our consciousness that we simply cannot wrap our minds around in any way (possibly because we're hallucinating it).
So yes, I would bite the bullet on this: consciousness could emerge from placing rocks in a certain pattern following instructions in a book. It would just be an excruciatingly "slow" consciousness.