The closest thing to a credible threat from space would be a large asteroid, since we, you know, already had at least one in history. But generally, with or without humans, mass death events in the last 4 billion years have been overwhelmingly coming from good on earth, not up there.
Well, an alien lifeform might not have the compassion a human is capable of, nor do they have the risk of mutual self-destruction. Aliens would have no problem using a planet cracker on earth for our iron core if they wanted it and were capable.
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