Um, just putting this out there, but isn't assuming sentient races from other worlds want to abduct us and perform experiments upon us kinda xenophobic? Of course, our race is naturally xenophobic by nature (aka racism, sexism, nationalism, hell, the world alien basically means foreign). Also, if a sentient race has developed technologically to the point where they can travel to another solar system in a reasonable amount of time I don't think they would have any interest in our world to be honest (which is polluted and overpopulated). Interstellar travel is a level of technology our race can only dream of right now and if another race managed to develop it I'm betting they also have the power to reorganize matter into anything they'd want or need (aka replicators from Star Trek). They would be on a level so advanced we would seem barbaric by comparison.