The trick for the species is to get off planet to the infinite resources in the wider galaxy, in which case it isn't short term gains. It might suck for individuals and the ecosystems destroyed.
We can't even live sustainably on the planet we evolved to thrive on for millions of years and people think we'll just terraform a whole or planet/solar system/galaxy...
Living sustainably has little to do with expansion of the species (and population, pretty much by definition). Almost the opposite. Maybe the solution to Fermi's Paradox being discussed is other species do become fully sustainable and thus never spread. Leaving us with the opportunity to devour the galaxy like a cancer.
