> It also means that over time, the Darwinian pressure is for us to become ever more good, as that is what gets rewarded. Therefore, if one day we meet powerful aliens, they are likely ethical aliens.

I can't agree with this kind of reasoning. Evolution doesn't have direction, there's no such thing as "good" in this process. Even historically some factors made certain level of cooperation better for survival it doesn't mean it'll be true forever and the balance is always shifting even in recent history. And aliens is guaranteed to have a vastly different "evolution" history than us, using the word "ethical" is nonsense.