I like Dr. Neil deGrasse Tyson's response. That in order for an alien civilization that has the power to travel throughout space, having  that level of power, would have to have evolved to be cooperative otherwise that species would end up destroying itself before it could even leave it's solar system.,(reply>), Cooperative doesn't mean peaceful.  Imagine Hitler winning WWII after some of his scientists invented technology that can do space travel.  He then killed everyone on earth who are not German and proceed to travel the galaxy to look for other resources.