I'll start with this, because it should help with the other item. We know there are two identical consciousnesses exactly because they are separate in spacetime. That is, while I can send the same input to both and get the same mind, that's not the interesting thing. The interesting thing is that I also can send different inputs, and then I'll get different minds. If it really were a single consciousness, that would be impossible. For example, you can't feed me both pure redness and pure greenness at the same time, so I am a single consciousness.

Here is where we get back to the first item: if we accepted that qualia are not localized in spacetime, we'd have to accept that there is no difference between me experiencing redness and you experiencing redness. Even if you consider that your qualia are separate from my own because of our different contexts, that still doesn't fully help: perhaps two different beings on two different planets happen to lead identical lives up to some point when a meteorite hits one of the planets and gravely injures one of their bodies. Would you say that there was a single consciousness that both bodies shared, but that it suddenly split once the meteorite hit?

Now, that is a valid position to take, in some sense. But then that means that consciousness is not continuous in any way, in your view. The day the meteorite hit planet A is not special in any way for planet B. So, if the single consciousness that planet A and planet B shared stopped that day, only to give rise to two different consciousnesses, that means that this same phenomenon must happen every day, and in fact at every instant of time. So, we now must accept that any feeling of time passing must be a pure illusion, since my consciousness now is a completely different consciousness than then one that experienced the previous minute. While this is a self-consistent definition, it's much more alien than the alternative - where we would accept that consciousness is tied in spacetime to its substrate.