Sustainability is an over hyped and misunderstood term.
Does this activity add to the likelihood that humanity will cease to enjoy a standard of living similar to the current average at some point before other natural processes (Sun going red giant, etc.) kill us all anyway?
So hey, if they sun's gonna kill us all next year, go hog wild. If what I'm doing now means that somebody 500 years from now will have a more impoverished existence, it's not.
Advanced species lifespan seems to range from ~1 - 10 million years or so, plus or minus a lot, before genetic drift sets in.
Three hundred mega-years (what I meant) is a somewhat arbitrary milestone. (I think long-term but 10^15 years is a bit much for even me. But see Stapledon's "Star Maker"...)
(BTW, your thinking seems unusually clear on these matters.)