I keep seeing you repeat that view, and I must say that I find it an odd one. Ethics is based on sentience and self-awareness, and a concept of rights, not whether one is an alien or not.
Are you saying that if an alien species of intelligent advanced beings were discovered, ethics wouldn't apply to them?
I am not saying that we should fly out there and deny who we are. We should certainly stand behind our values and apply them.
Most of the times this is probably not a problem, when you meet a ship in distress you help those folks.
But when you meet e.g. folks like the Klingons you encounter a species that is in many ways the literal opposite of yourself. You are life-loving and democratic, they are death-loving and aristocratic. If we were on Earth I would not hesitate to say that they have to be crushed (ideologically) as they violate our universal principles. But in space this is not possible unless you wanna wage war against them.
What actually happened, a fragile alliance after centuries of conflict with somebody who is so very unlike yourself, is the better way.
Obviously I am not caring about pragmatic solutions but about the radical implications of ethics. Down here slavery is something which has to be crushed as it violates an absolute human value. But not up there as we have no right to postulate our human absolutes as universally, galaxy-wide absolutes. If everybody did that this would lead to total war.
So in my opinion the very absoluteness of our values paradoxically forbids us from applying them to other species. Naturally a more pragmatic view upon ethics would come to different conclusions.