Well, while they're still dominant, all the other cultures might decide to band together and discourage, eradicate or dilute the one that keeps growing.
Anyway I agree that we can't say for certain whether population will grow or shrink. In fact in the context of this discussion I think that's the most important point. Many discussions about alien civilizations tend to assume that they'll evolve into huge multiplanetary populations with large energy/EM/whatever footprints. When in reality our most developed cultures are slowly declining in population. If an underground cache of brains in pleasure boxes is the end stage for most civs we will probably never know.
That's a good point, and one I often wonder about too. Maybe advanced civilizations are not expansionist. However it doesn't make a good solution to Fermi's Paradox because all civilizations would have to not be expansionist, if there were just a few exceptions they'd expand all over and we'd likely spot them.
Anyway I agree that we can't say for certain whether population will grow or shrink. In fact in the context of this discussion I think that's the most important point. Many discussions about alien civilizations tend to assume that they'll evolve into huge multiplanetary populations with large energy/EM/whatever footprints. When in reality our most developed cultures are slowly declining in population. If an underground cache of brains in pleasure boxes is the end stage for most civs we will probably never know.