Sustainable is well defined (don't consume more than the earth can generate), but it is abused by marketers for green washing.

OK, here's my own definition:

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.

Will there still be humans in 300,000,000 million years?

300 trillion? Unlikely.

Derp. My bad.

So what did you mean? And what are you getting at?

Advanced species lifespan seems to range from ~1 - 10 million years or so, plus or minus a lot, before genetic drift sets in.

I took a bit of umbrage at the idea that humans surviving longer than, say, the dinosaurs did is "over hyped and misunderstood". That comment was my attempt at an unhyped and easily understood definition of "sustainability".

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.)