Alien invasion imminent (in galactic time)?

If the SETI (Search for Extraterrestrial Intelligence) Institute in California gets its way, we'll be inviting aliens to Earth. I think this is an extremely bad idea. While the chances are extremely remote that we'd see a single space craft in Earth orbit any time soon, I come down on the side of the sci-fi camp that says the only reason to make such an interstellar journey is for the resources along the way. And civilizations capable of making such a journey will more than likely not be benevolent. Even the alien refugees or whatever they were in the brilliant District 9 film had weapons and avionics technology superior to ours. And while we managed to contain them, only because there ship was somehow temporarily disabled, the film's ending seemed to portend a rescue and retribution scenario.