Logical reasoning tells us that if an alien race was to make itself known and travel all the way to our world it would be purely for conquest. Were already advanced enough to know how unique our world is and we ourselves have already had talks regarding the colonization of other planets. Now regardless of whether we will be able to do this anytime soon that should give us an idea of what we would be dealing with. Any gentle race of extra-terrestials would steer clear of us. Maybe they'd document us to satisfy there own quest for knowledge, but if tommorow there were a million ships hovering our planet in plain sight we could know for certain they mean us harm. Any intelligent and gentle race would have known to phone ahead and at least let us know they're coming ;)