At this moment in time I think it would be unwise for humans to try and contact aliens. I agree with an earlier comment by THE SILENT MAJORITY, we should spread ourselves before we initiate contact. Even it was a peaceful alien specices to meet us, who is to say that they dont carry diseases that they dont even know of, or maybe theyr'e ships emit gas that is poisonous to the planet. There could be a number of things that go wrong and destroy the planet. Why would we take the risk before having a fall back. If they were advanced enough to find us and violent a back up plan might be a moot point, but why chance it?