Well we can't assume we know physics completely yet (or within bounds of the question) something down the road may open an idea or ability to generate more power than we know what to do with. If this was a game we may only been on the first or second step of a technology tree. Or we just aren't able to travel that far realistically, we have to overcome our idea of our species being singular and send out generation ships that go for ages (in human time) to explore more as a species, even if the originators (Earth humans) may never know the outcome.

Of course if we discover that much power we'd likely annihilate ourselves anyways, least with our current society.

I do mostly agree but I try and think of other possibilities since the universe is so vast.