This is getting silly.
"(I notice that you have left out this point completely)"
No, I didn't. I addressed it in the other half of my post, which you obviously saw since you responded to it. If every sentence must address all parts of the argument, we're all guilty of flagrant violations up and down this thread (and every other) and will need to be writing some awfully convoluted sentences.
"What of it we can access, and what use we can make of it [...] at this point in time is limited by our past light cone and our current knowledge and technology, obviously. But what of it we can access, and what use we can make of it, indefinitely into the future is not; it is only limited by the entire universe and our future knowledge and technology."
Per my understanding of relativity and the present state of physics (significantly received from others but I think that I followed it at the time) this is simply not the case (in particular, if time is finite then "everything our light cone will encompass before the end of time" is finite - and I think an expansionary universe makes things worse). I think we're going to need to bust out some math or expert testimony instead of simply making assertions at each other if we're going to get anywhere.
"For any specific task undertaken at a specific point in time, in a specific, fixed state of knowledge and technology, yes, there is such a bound in principle; but you made a much stronger claim than that."
There is a set of possible futures from any present. You hold that, for any task in any situation, with sufficient knowledge, the resources it can take can approach arbitrarily close to zero?
'Also, whether or not that in principle limit has practical significance even over "short" time scales such as a human lifetime depends on how fast our technology and knowledge changes, not just on what they are at a given instant.'
I don't think the bounds given by physics have any impact yet. I'm not convinced they ever will - my point was there is a theoretical bound, and there may be more practical bounds that matter at any time-scale.
Let's try to get this back closer to useful.
My original point, which I think too much was read into, was simply that there are situations in which some having more can lead to others having less, and that paying attention to whether we're in such a situation is worthwhile. I stated right there in that first comment that I didn't think we presently were, in most respects.
That was followed by a levelling of a charge of "zero-sum thinking" in an explicitly hypothesized zero-sum situation, which (again) I said I thought unlikely to be relevant. I found this amusing.