[ImSkeptical]

I don't think we should try to guess the motivations of aliens. You can't really rule out, or make well founded assumptions about, how aliens will act or what they'll want.

Perhaps the aliens will just exterminate us to foreclose on the possible future where we become their equal or better. Perhaps they'll kill us for religious or ideological reasons. Perhaps they'll have a need to do something with our resources and no concern for our well being. Perhaps they'll be intelligent weapon systems programmed to kill and they'll identify us as enemies.